Use bazel syntax for fully qualified name in path property

A module reference to a fully qualified module in a path property looks
like:
  //path:module
And with a tag:
  //path:module{tag}

At the moment the checking is quite lax but some follow up changes will
make it much stricter.

Bug: 193228441
Test: m nothing
Change-Id: Ie42edcfa33ec66fda5d75b3df1da73f56f147afd