Draft: Add codefix scaffold for undeclared private method

[dannikrauser]

This pull request is related to Issue #37782.

Hi, I am workingon this as part of a software enigneering class project. My goal is to begin implementing a quick fix that declares a missing private method when it’s referenced but not yet defined. My focus is on understanding the TypeScript codefix structure and documenting the setup/learning process.

This is a draft/in-progress pull request. The current implementation includes placeholder logic inside addMissingMethod.ts under src/services/codefixes/. The current code does not yet attach to a real error code.

Open to any feedback!

[typescript-bot]

With 6.0 out as the final release vehicle for this codebase, we're closing all PRs that don't fit the merge criteria for post-6.0 patches. If you think this was a mistake and this PR fits the post-6.0 patch criteria, please post to the 6.0 iteration issue with details (specifically, which PR and which patch criteria it satisfies).

Next steps for PRs:

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