[WIP] Fix type parameter default ignored in callback

[Copilot]

Fixes #63949

Analysis

• Locate the TS 7 inference path that discards the defaulted type argument during contextual callback checking.
• Add a focused compiler regression test based on the minimized repro.
• Apply the smallest checker fix and validate targeted behavior.
• Run required build, test, lint, and format commands; review and security-scan the final change.

Fix

Pending investigation.

Copilot Checklist

I successfully ran these commands at the end of my session, and they completed without error:

• npx hereby build
• npx hereby test
• npx hereby lint
• npx hereby format

• Fixes [7.0 regression] Type parameter default is ignored when the call sits inside a callback passed to a generic function #63949