fix(ngcc): correctly get config for sub-entry-points when primary entry-point is ignored (#37040)

Previously, when an entry-point was ignored via an ngcc config, ngcc
would scan sub-directories for sub-entry-points, but would not use the
correct `packagePath`. For example, if `@angular/common` was ignored, it
would look at `@angular/common/http` but incorrectly use
`.../@angular/common/http` as the `packagePath` (instead of
`.../@angular/common`). As a result, it would not retrieve the correct
ngcc config for the actual package.

This commit fixes it by ensuring the correct `packagePath` is used, even
if the primary entry-point corresponding to that path is ignored. In
order to do this, a new return value for `getEntryPointInfo()` is added:
`IGNORED_ENTRY_POINT`. This is used to differentiate between directories
that correspond to no or an incompatible entry-point and those that
correspond to an entry-point that could otherwise be valid but is
explicitly ignored. Consumers of `getEntryPointInfo()` can then use this
info to discard ignored entry-points, but still use the correct
`packagePath` when scanning their sub-directories for secondary
entry-points.

PR Close #37040

packages/compiler-cli/test/helpers/src/mock_file_loading.ts

@@ -37,7 +37,7 @@ export function loadStandardTestFiles(
     loadFakeCore(tmpFs, basePath);
   } else {
     getAngularPackagesFromRunfiles().forEach(({name, pkgPath}) => {
-      loadTestDirectory(tmpFs, pkgPath, tmpFs.resolve('/node_modules/@angular', name));
+      loadTestDirectory(tmpFs, pkgPath, tmpFs.resolve(basePath, 'node_modules/@angular', name));
     });
   }