rust-indexer: Handle better trait function impls.
rust-indexer: Handle better trait function impls.

This allows finding all the trait implementations from a trait function with a
single click.

Before this, in the test code, for example, for the "fn do_bar" line in
"impl MyTrait for Loader" we get the following symbol:

  simple<Loader as test_rust_dependency::MyTrait>::do_bar

This is fine, but we also want to get:

  test_rust_dependency::MyTrait::do_bar

So we can relate all the impls of the same function for the trait.

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