Decide if new analyzer API needs a way to override UriConverter

[stereotype441]

As mentioned in code review, the new analyzer API replaces the UriResolver class with UriConverter, but it doesn't provide a way for clients to override the choice of UriConverter or supply their own class implementing the interface. However, at least two existing clients in build contain subclasses of UriResolver:

• bazel_codegen (2 classes named BuildAssetUriResolver)
• build_resolvers (1 class named _AssetUriResolver)
  There may be other uses in the Google internal codebase.

We need to understand the use cases for these client classes and ensure that the new analyzer API supports them.