Implement name and identifier size limits

[pinodeca]

From docs/proposals/size-limits.md in branch pinodeca/size-limits (associated with PR #14 - #14), implement phases 1a and 2 and submit a single PR.

Phase 1a - minimum scaffolding for name/ID limits (no behavior change).
Phase 2 - name and identifier size limits.

The size-limits.md file can be found at:

• https://github.com/microsoft/duroxide/blob/07136051de0486ee2f0ecf5793e5ac6bafca400b/docs/proposals/size-limits.md
• https://github.com/microsoft/duroxide/blob/pinodeca/size-limits/docs/proposals/size-limits.md
• or by checking out branch pinodeca/size-limits
• or by cherry-picking commit 0713605