Introduce AssetOrArchive to support the SDK's Asset type which can be both (#242)

Resolves #237.

This PR addresses an issue with the design of the [assets and archives
support](https://www.pulumi.com/docs/concepts/assets-archives/) in
Pulumi core. Quoting #237:

> When defining a property of type resource.Asset, the generated schema
will contain a $ref of pulumi.json#/Asset. However, in the SDKs, an
"asset" is represented by pulumi.AssetOrArchive because an archive is
currently always a valid asset.

> Therefore, when deserializing the PropertyValue for the provider to
use, it's valid for the user to have specified one of the Archive types
which then isn't deserializable into the resource.Asset field within the
provider.

To work around this, we define a new type `types.AssetOrArchive` here in
pulumi-go-provider. In the schema, it's represented as a standard
`pulumi.json#/Asset` for interoperability. An incoming core `Asset` is
translated into a `types.AssetOrArchive`, in `Decode`, with either Asset
or Archive populated. Vice versa, `Encode` pulls the asset/archive out
of AssetOrArchive.

## Notes
- The decode and encode implementations are bespoke and there might be
opportunities to move it to a new, more generic extension point.

---------

Co-authored-by: Ian Wahbe <[email protected]>

Author: thomas11

examples/assets/consumer/Pulumi.yaml

@@ -0,0 +1,16 @@
+name: consume-assets
+runtime: yaml
+
+plugins:
+  providers:
+    - name: assets
+      path: ..
+
+resources:
+  assetsResource:
+    type: assets:HasAssets
+    properties:
+      a1:
+        fn::fileAsset: ./file.txt
+      a2:
+        fn::fileArchive: ./file.txt.zip

examples/assets/consumer/file.txt

@@ -0,0 +1 @@
+foo

examples/assets/consumer/file.txt.zip

@@ -0,0 +1,97 @@
+module github.com/pulumi/pulumi-go-provider/examples/assets
+
+replace github.com/pulumi/pulumi-go-provider => ../..
+
+go 1.22.4
+
+require github.com/pulumi/pulumi-go-provider v0.0.0-00010101000000-000000000000
+
+require (
+	dario.cat/mergo v1.0.0 // indirect
+	github.com/Microsoft/go-winio v0.6.1 // indirect
+	github.com/ProtonMail/go-crypto v1.0.0 // indirect
+	github.com/aead/chacha20 v0.0.0-20180709150244-8b13a72661da // indirect
+	github.com/agext/levenshtein v1.2.3 // indirect
+	github.com/apparentlymart/go-textseg/v13 v13.0.0 // indirect
+	github.com/atotto/clipboard v0.1.4 // indirect
+	github.com/aymanbagabas/go-osc52/v2 v2.0.1 // indirect
+	github.com/blang/semver v3.5.1+incompatible // indirect
+	github.com/charmbracelet/bubbles v0.16.1 // indirect
+	github.com/charmbracelet/bubbletea v0.24.2 // indirect
+	github.com/charmbracelet/lipgloss v0.7.1 // indirect
+	github.com/cheggaaa/pb v1.0.29 // indirect
+	github.com/cloudflare/circl v1.3.7 // indirect
+	github.com/containerd/console v1.0.4-0.20230313162750-1ae8d489ac81 // indirect
+	github.com/cyphar/filepath-securejoin v0.2.4 // indirect
+	github.com/djherbis/times v1.5.0 // indirect
+	github.com/edsrzf/mmap-go v1.1.0 // indirect
+	github.com/emirpasic/gods v1.18.1 // indirect
+	github.com/go-git/gcfg v1.5.1-0.20230307220236-3a3c6141e376 // indirect
+	github.com/go-git/go-billy/v5 v5.5.0 // indirect
+	github.com/go-git/go-git/v5 v5.12.0 // indirect
+	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/golang/glog v1.2.0 // indirect
+	github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/grpc-ecosystem/grpc-opentracing v0.0.0-20180507213350-8e809c8a8645 // indirect
+	github.com/hashicorp/errwrap v1.1.0 // indirect
+	github.com/hashicorp/go-multierror v1.1.1 // indirect
+	github.com/hashicorp/hcl/v2 v2.17.0 // indirect
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/jbenet/go-context v0.0.0-20150711004518-d14ea06fba99 // indirect
+	github.com/kevinburke/ssh_config v1.2.0 // indirect
+	github.com/lucasb-eyer/go-colorful v1.2.0 // indirect
+	github.com/mattn/go-isatty v0.0.19 // indirect
+	github.com/mattn/go-localereader v0.0.1 // indirect
+	github.com/mattn/go-runewidth v0.0.15 // indirect
+	github.com/mitchellh/go-ps v1.0.0 // indirect
+	github.com/mitchellh/go-wordwrap v1.0.1 // indirect
+	github.com/muesli/ansi v0.0.0-20230316100256-276c6243b2f6 // indirect
+	github.com/muesli/cancelreader v0.2.2 // indirect
+	github.com/muesli/reflow v0.3.0 // indirect
+	github.com/muesli/termenv v0.15.2 // indirect
+	github.com/natefinch/atomic v1.0.1 // indirect
+	github.com/opentracing/basictracer-go v1.1.0 // indirect
+	github.com/opentracing/opentracing-go v1.2.0 // indirect
+	github.com/pgavlin/fx v0.1.6 // indirect
+	github.com/pgavlin/goldmark v1.1.33-0.20200616210433-b5eb04559386 // indirect
+	github.com/pjbgf/sha1cd v0.3.0 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
+	github.com/pkg/term v1.1.0 // indirect
+	github.com/pulumi/appdash v0.0.0-20231130102222-75f619a67231 // indirect
+	github.com/pulumi/esc v0.6.2 // indirect
+	github.com/pulumi/pulumi/pkg/v3 v3.117.0 // indirect
+	github.com/pulumi/pulumi/sdk/v3 v3.117.0 // indirect
+	github.com/rivo/uniseg v0.4.4 // indirect
+	github.com/rogpeppe/go-internal v1.11.0 // indirect
+	github.com/sabhiram/go-gitignore v0.0.0-20210923224102-525f6e181f06 // indirect
+	github.com/santhosh-tekuri/jsonschema/v5 v5.0.0 // indirect
+	github.com/segmentio/asm v1.1.3 // indirect
+	github.com/segmentio/encoding v0.3.5 // indirect
+	github.com/sergi/go-diff v1.3.2-0.20230802210424-5b0b94c5c0d3 // indirect
+	github.com/skeema/knownhosts v1.2.2 // indirect
+	github.com/spf13/cobra v1.8.0 // indirect
+	github.com/spf13/pflag v1.0.5 // indirect
+	github.com/texttheater/golang-levenshtein v1.0.1 // indirect
+	github.com/tweekmonster/luser v0.0.0-20161003172636-3fa38070dbd7 // indirect
+	github.com/uber/jaeger-client-go v2.30.0+incompatible // indirect
+	github.com/uber/jaeger-lib v2.4.1+incompatible // indirect
+	github.com/xanzy/ssh-agent v0.3.3 // indirect
+	github.com/zclconf/go-cty v1.13.2 // indirect
+	go.uber.org/atomic v1.10.0 // indirect
+	golang.org/x/crypto v0.23.0 // indirect
+	golang.org/x/exp v0.0.0-20231110203233-9a3e6036ecaa // indirect
+	golang.org/x/mod v0.14.0 // indirect
+	golang.org/x/net v0.25.0 // indirect
+	golang.org/x/sync v0.6.0 // indirect
+	golang.org/x/sys v0.20.0 // indirect
+	golang.org/x/term v0.20.0 // indirect
+	golang.org/x/text v0.15.0 // indirect
+	golang.org/x/tools v0.17.0 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20240415180920-8c6c420018be // indirect
+	google.golang.org/grpc v1.63.2 // indirect
+	google.golang.org/protobuf v1.33.0 // indirect
+	gopkg.in/warnings.v0 v0.1.2 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+	lukechampine.com/frand v1.4.2 // indirect
+)