Fix dynamic imports in google ads vendored in library (#30544)

This is a further fix to vendor-in google-ads library:

* moving from _vendor to google_vendor is needed to keep
  the tree structure separate from `google` package used
  in google provider. If we do not do that, ads library
  will find "google" package when walking up the tree
  and will determine that this is the "top" google package

* dynamic imports of ads library imports have been updated
  to also import from the vendored-in library

* only v12 version is supported

Closes: #30526