This commit removes `@angular-devkit/build-angular` from package.json
for a project that opts into Bazel. This is because the package adds a
dependency on node-sass, which is rejected by Bazel due to its absense.
This commit also appends to `scripts.postinstall` if it already exists.
This is needed because `ng new` in CLI v9 now automatically adds a
postinstall step for `ngcc`.
PR Close#32946