api_proto_plugin: Add `protoshared` aspect (#22007)

This cycles proto deps and creates a descriptor file from them.

This will allow other proto plugins to call protoc with the descriptor
file and just their `direct_sources` and not all of the `transitive_sources`

Signed-off-by: Ryan Northey <ryan@synca.io>

Mirrored from https://github.com/envoyproxy/envoy @ 00aab5c9c89b16435633613e5e57374f28cd7e26

bazel/api_build_system.bzl

@@ -11,6 +11,8 @@ load(
     "EXTERNAL_PROTO_PY_BAZEL_DEP_MAP",
 )
 
+EnvoyProtoDepsInfo = provider(fields = ["deps"])
+
 _PY_PROTO_SUFFIX = "_py_proto"
 _CC_PROTO_SUFFIX = "_cc_proto"
 _CC_GRPC_SUFFIX = "_cc_grpc"