Don't try to narrow type of a symbol within RHS of its declaration

[Andarist]

fixes #62993
fixes #63044
fixes #63091
fixes #63093
it's using an alternative approach to microsoft/typescript-go#2542

[jakebailey]

Do we need a different approach? Or can we just match? (Why the difference?)

[Andarist]

Strada can certainly match the Corsa’s patch. It’s just this PR predates the Corsa’s PR and given I managed to get rid of an existing node flag here, I figured out it might be interesting to leave it for review. Feel free to close this though.

[jakebailey]

Oh, I just want them to match; I don't think that a method that saves us a flag is bad, just trying to understand how to align things.

[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:

• For crash bugfixes or language service improvements, PRs are currently accepted at the typescript-go repo
• Changes to type system behavior should wait until after 7.0, at which point mainline TypeScript development will resume in this repository with the Go codebase
• Library file updates (lib.d.ts etc) continue to live in this repo or the DOM Generator repo as appropriate