Within an Angular package, it can happen that there are
entry-points which do not contain features that belong into
an `@NgModule` or need metadata files to be generated.
For example: the `cdk`, `cdk/testing` and `cdk/coercion`
entry-points. Besides other entry-points in the `cdk`
package, those entry-points do not need metadata to
be generated and no not use the `ng_module` rule.
Currently the "ng_package" rule properly picks up such
entry-points and builds bundles, does downleveling etc.
The only thing it misses is that no `package.json` files
are generated for the entry-point. This means that consumers
will not be able to use these entry-points built with "ts_library"
(except accessing the individual bundlings explicitly).
The "ng_package" rule should follow the full APF specification
for such entry-points. Partially building bundles and doing the
downleveling is confusing and a breaking issue.
The motifivation of supporting this (besides making the
rule behavior consistent; the incomplete output is not
acceptable), is that using the "ng_module" rule does
not make sense to be used for non-Angular entry-points.
Especially since it depends on Angular packages to
be specified as Bazel action inputs just to compile
vanilla TypeScript with `@angular/compiler-cli`.
PR Close#32610
