Supports creating enum value as a gRPC Federation's variable

[goccy]

Supports the following features.

• def { name: "v" enum { name: "MyEnum" by: "dep.Enum.ENUM_VALUE_1" }}
• def { map { iterator { name: "iter" src: "types" } enum { name: "MyEnum" by: "iter" } } }

[github-actions]

Code Metrics Report

	main (aaa31df)	#257 (a37b3ee)	+/-
Coverage	65.6%	65.8%	+0.3%
Code to Test Ratio	1:0.4	1:0.4	-0.0
Test Execution Time	8m9s	8m17s	+8s

Details

  |                     | main (aaa31df) | #257 (a37b3ee) |  +/-  |
  |---------------------|----------------|----------------|-------|
+ | Coverage            |          65.6% |          65.8% | +0.3% |
  |   Files             |             76 |             76 |     0 |
  |   Lines             |          12787 |          12991 |  +204 |
+ |   Covered           |           8387 |           8554 |  +167 |
- | Code to Test Ratio  |          1:0.4 |          1:0.4 |  -0.0 |
  |   Code              |          39681 |          40275 |  +594 |
+ |   Test              |          15435 |          15548 |  +113 |
- | Test Execution Time |           8m9s |          8m17s |   +8s |

Code coverage of files in pull request scope (78.2% → 78.3%)

Files	Coverage	+/-
generator/code_generator.go	78.0%	+0.5%
grpc/federation/generator/decode.go	73.4%	+0.1%
grpc/federation/generator/encode.go	82.2%	-0.0%
internal/testutil/builder.go	84.8%	+0.3%
resolver/def.go	93.8%	+0.0%
resolver/enum.go	86.4%	+1.4%
resolver/format.go	89.6%	-0.2%
resolver/message.go	75.5%	+0.6%
resolver/resolver.go	83.3%	-0.1%
resolver/types.go	86.7%	0.0%
source/clone.go	76.4%	+0.6%
source/file.go	65.0%	-0.1%
source/location.go	0.0%	0.0%
source/location_builder.go	68.8%	+0.3%

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Reported by octocov