Move md_get_pdb_id to dnmd_pdb.h and reduce CI matrix

[AaronRobinsonMSFT]

Changes

Move md_get_pdb_id to dnmd_pdb.h and fix size query pattern

• Move the md_get_pdb_id declaration from dnmd.h to dnmd_pdb.h where it belongs alongside other Portable PDB APIs.
• Fix the implementation to always write back the required buffer size before checking if the caller's buffer is large enough, enabling callers to query the needed size with a too-small buffer.

Reduce CI matrix to sparse configuration

Replace the full 12-leg matrix (3 OS × 2 flavors × 2 vendored) with a sparse 8-leg matrix to reduce CI costs while maintaining coverage:

• Ubuntu: Debug and Release, both vendored modes (4 legs)
• macOS: Debug vendored, Release non-vendored (2 legs)
• Windows: Release vendored, Debug non-vendored (2 legs)
• Sanitizers: unchanged (Ubuntu Debug)

[Copilot]

Pull request overview

This PR refactors the public Portable PDB API surface by relocating md_get_pdb_id into the Portable PDB header, updates md_get_pdb_id to support “size query” usage by always writing back the required length, and reduces the GitHub Actions build matrix to a smaller set of representative configurations.

Changes:

• Move the md_get_pdb_id declaration from dnmd.h to dnmd_pdb.h.
• Update md_get_pdb_id to write the required *pdb_id_len before rejecting an undersized buffer.
• Reduce CI build matrix legs using an explicit matrix.include list.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/inc/dnmd_pdb.h	Adds the md_get_pdb_id declaration alongside other Portable PDB APIs.
src/inc/dnmd.h	Removes the md_get_pdb_id declaration from the core public header.
src/dnmd/entry.c	Adjusts md_get_pdb_id to support size-query semantics (but currently needs a safety fix).
.github/workflows/main.yml	Switches to a sparse CI matrix to reduce total jobs while keeping coverage.

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