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

rust/testing.go

@@ -79,6 +79,13 @@ func GatherRequiredDepsForTest() string {
 			nocrt: true,
 			system_shared_libs: [],
 		}
+		cc_library {
+			name: "libprotobuf-cpp-full",
+			no_libcrt: true,
+			nocrt: true,
+			system_shared_libs: [],
+			export_include_dirs: ["libprotobuf-cpp-full-includes"],
+		}
 		rust_library {
 			name: "libstd",
 			crate_name: "std",
@@ -103,6 +110,18 @@ func GatherRequiredDepsForTest() string {
 			srcs: ["foo.rs"],
 			host_supported: true,
 		}
+		rust_library {
+			name: "libgrpcio",
+			crate_name: "grpcio",
+			srcs: ["foo.rs"],
+			host_supported: true,
+		}
+		rust_library {
+			name: "libfutures",
+			crate_name: "futures",
+			srcs: ["foo.rs"],
+			host_supported: true,
+		}
 
 ` + cc.GatherRequiredDepsForTest(android.NoOsType)
 	return bp