rust_grpcio well known types support, default deps

The usage of the well known type Empty requires a hack in the module
above the grpc implementation, this is now the generated stem_mod.rs

This also adds additional implicit dependencies that are required by
the grpc protobuf generated code. This includes the addition of a
'header_libs' property for library dependencies which export include
paths required by protos.

We also now include both the protos and the grpcio in the library
variant via the mod_stem.rs.

Bug: 172592789
Bug: 171504899
Test: m nothing
Test: Example rust_grpcio module build command includes dependencies,
      include paths.
Change-Id: I187a13cd5cdea991828a1020314de16727e4f74e
diff --git a/cc/cc.go b/cc/cc.go
index 3297e41..349d03d 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -579,6 +579,11 @@
 	return ok && ccLibDepTag.static()
 }
 
+func IsHeaderDepTag(depTag blueprint.DependencyTag) bool {
+	ccLibDepTag, ok := depTag.(libraryDependencyTag)
+	return ok && ccLibDepTag.header()
+}
+
 func IsRuntimeDepTag(depTag blueprint.DependencyTag) bool {
 	ccDepTag, ok := depTag.(dependencyTag)
 	return ok && ccDepTag == runtimeDepTag