The dynamically compiled ESM import helper is now cached to prevent the need
to recompile the helper function everytime a load ESM helper call is made.
This helper is currently used to workaround dynamic import limitations with
the TypeScript compilation output. Once the build process is updated, it will
no longer be required.
Absolute import paths, especially on Windows, must be `file://` URLs when using ESM. Otherwise, Windows drive letters (e.g., `C:`) would be interpreted as a protocol instead of a drive letter when performing the import.
This is a followup PR for #21771 that addresses partial compilation linker usage.
With the Angular CLI currently being a CommonJS package, this change uses a dynamic import to load `@angular/compiler-cli/linker[/babel]` which may be ESM. CommonJS code can load ESM code via a dynamic import. Unfortunately, TypeScript will currently, unconditionally downlevel dynamic import into a require call. require calls cannot load ESM code and will result in a runtime error. To workaround this, a Function constructor is used to prevent TypeScript from changing the dynamic import. Once TypeScript provides support for keeping the dynamic import this workaround can be dropped and replaced with a standard dynamic import.
