Add support for package_alias in crate.spec (bzlmod) (#3743)

Closes #3742 

This makes using different versions of the same crate easier.

Author: nmattia

crate_universe/extensions.bzl

@@ -1161,7 +1161,7 @@ def _crate_impl(module_ctx):
                 manifests = {str(module_ctx.path(m)): str(m) for m in cfg.manifests}
 
             packages = {
-                p.package: _package_to_json(p)
+                p.package_alias or p.package: _package_to_json(p)
                 for p in common_specs + repo_specific_specs.get(cfg.name, [])
             }
 
@@ -1431,6 +1431,9 @@ _spec = tag_class(
             doc = "The explicit name of the package.",
             mandatory = True,
         ),
+        "package_alias": attr.string(
+            doc = "Alias for the package.",
+        ),
         "path": attr.string(
             doc = "The local path of the remote crate. Cannot be used with `version` or `git`.",
         ),

examples/crate_universe/MODULE.bazel

@@ -515,6 +515,13 @@ no_cargo.spec(
     repositories = ["no_cargo"],
     version = "0.4",
 )
+no_cargo.spec(
+    features = ["util"],
+    package = "tower",
+    package_alias = "tower_new",  # used in package_alias test
+    repositories = ["no_cargo"],
+    version = "0.5.3",
+)
 no_cargo.spec(
     features = ["trace"],
     package = "tower-http",

examples/crate_universe/package_alias/BUILD.bazel

@@ -0,0 +1,4 @@
+alias(
+    name = "tower-new",
+    actual = "@no_cargo//:tower_new",  # ensures the package_alias works
+)