Add in-proc debugger load proposal

[AaronRobinsonMSFT]

Summary

• add the new in-proc-debugger-load.md proposal under proposed
• index the proposal in INDEX.md
• capture the host-controlled in-proc debugger load hook design for non-desktop hosts

[Copilot]

Pull request overview

Adds a new design proposal documenting a host-controlled mechanism for loading an in-process native debugger/diagnostics library after runtime initialization but before the first managed instruction executes, primarily for mobile/non-desktop hosts.

Changes:

• Added a new proposal doc: proposed/in-proc-debugger-load.md
• Updated INDEX.md to include the new proposal entry and owners

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
proposed/in-proc-debugger-load.md	New proposal describing scenarios, requirements, and a host-owned model for early in-proc debugger library loading.
INDEX.md	Adds the proposal to the Proposals table with owners.

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