CloneContext: Assert objects are owned by the program

Check that pre-clone objects are owned by the source program.
Check that post-clone object are owned by the target builder.

Fixed: tint:469
Change-Id: Idd0eeb8dfb386e295b66b4b6621cc13dc1a30786
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/48260
Commit-Queue: Ben Clayton <bclayton@chromium.org>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: James Price <jrprice@google.com>

src/program_builder.h

@@ -1505,6 +1505,12 @@ struct ProgramBuilder::TypesBuilder::CToAST<void> {
 };
 //! @endcond
 
+/// @param builder the ProgramBuilder
+/// @returns the ProgramID of the ProgramBuilder
+inline ProgramID ProgramIDOf(const ProgramBuilder* builder) {
+  return builder->ID();
+}
+
 }  // namespace tint
 
 #endif  // SRC_PROGRAM_BUILDER_H_