Add SourceProvider modules which provides a base interface for more
complex code generation usecases such as bindgen. Also adds the
rust_bindgen module type which calls bindgen to generate Rust FFI
bindings to C.
Bug: 159064919
Test: Local test module generates bindings.
Test: New Soong tests pass.
Change-Id: Ie31467bbbe423497666ad837cf5fe1acd1e76bd8
Ivan Lozano