Write template generation stats to trace output

To help debug 4mb size limit issues, it would be helpful to get an idea of:
- Nested module structure
- For each nested template (including main template): Number of characters, template hash

Please update this comment if you think of anything else.

The issue names no files, tests, or entry points. Start by locating template generation and trace-output handling in the Bicep repository, then determine how nested templates are represented and where generated diagnostics are emitted. Done means trace output exposes the requested nested structure, character counts, and hashes, with coverage for the resulting output.

Written by the indexing model from the issue text.