refactor(compiler-cli): implement BabelAstFactory and AstHosts (#38866)

This commit adds the `AstHost` interface, along with implementations for
both Babel and TS.

It also implements the Babel vesion of the `AstFactory` interface, along
with a linker specific implementation of the `ImportGenerator` interface.

These classes will be used by the new "ng-linker" to transform prelinked
library code using a Babel plugin.

PR Close #38866

.github/angular-robot.yml

@@ -47,6 +47,7 @@ merge:
       - "packages/bazel/src/ng_package/**"
       - "packages/bazel/src/protractor/**"
       - "packages/bazel/src/schematics/**"
+      - "packages/compiler-cli/linker/**"
       - "packages/compiler-cli/ngcc/**"
       - "packages/compiler-cli/src/ngtsc/sourcemaps/**"
       - "packages/docs/**"