Migrates `packages/core/schematics` to `ts_project`. As part of this,
this commit cleans up some of the mixed module types and tsconfigs in
the folder. A single tsconfig (and it's test variant) are now used.
For the shipped schematics, we explicitly use the `.cjs` extension, so
that the bundles are properly recognized as CommonJS; even if they are
part of the `type: module` `@angular/core` package.
The `package.json` with `type: commonjs` is removed from
`packages/core/schematics` as it's no longer needed given the explicit
extension & caused issues as schematics are compiled with ESM but are
only later bundled for shipping & some tests as ESM.
PR Close#61420