In certain cases, it is useful to share submessages across multiple parent messages.
proto2::cpp has a mechanism for this, so we add the hpb equivalent.
For this initial impl, we stipulate that the arenas must be exactly the same. We may explore broadening the constraint to allow for all fused arenas.
PiperOrigin-RevId: 681169537
This CL is mostly a no-op, except that now google3-only code is actually stripped from OSS, instead of being preserved in `# begin:google_only` blocks.
This follows the conventions of the greater Copybara ecosystem.
PiperOrigin-RevId: 669513564
This simplifies upb by removing differences between google3 and OSS.
This also points upb at the protobuf license, instead of keeping a separate copy around for upb.
PiperOrigin-RevId: 669447145