When ngtsc compiles @angular/core, it rewrites core imports to the
r3_symbols.ts file that exposes all internal symbols under their
external name. When creating the FESM bundle, the r3_symbols.ts file
causes the external symbol names to be rewritten to their internal name.
Under ngcc compilations of FESM bundles, the indirection of
r3_symbols.ts is no longer in place such that the external names are
retained in the bundle. Previously, the external name `ɵdefineNgModule`
was explicitly declared internally to resolve this issue, but the
recently added `setClassMetadata` was not declared as such, causing
runtime errors.
Instead of relying on the r3_symbols.ts file to perform the rewrite of
the external modules to their internal variants, the translation is
moved into the `ImportManager` during the compilation itself. This
avoids the need for providing the external name manually.
PR Close#27055
c8c8648abf