Fix data race via RequiresAddingImplicitUndefined

[jakebailey]

Fixes #1151

[Copilot]

Pull Request Overview

This PR introduces a mutex-protected public wrapper for RequiresAddingImplicitUndefined and refactors the underlying private logic to fix a data race.

• Adds RequiresAddingImplicitUndefined with locking in emitresolver.go
• Renames and refactors the original logic into requiresAddingImplicitUndefined and requiresAddingImplicitUndefinedWorker
• Updates the builder to call the (now private) requiresAddingImplicitUndefined

Reviewed Changes

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

File	Description
internal/checker/nodebuilderimpl.go	Calls the private requiresAddingImplicitUndefined instead of the public, locked wrapper
internal/checker/emitresolver.go	Adds a locked public RequiresAddingImplicitUndefined and refactors private methods

Comments suppressed due to low confidence (1)

internal/checker/nodebuilderimpl.go:1901

• This call bypasses the mutex by invoking the private requiresAddingImplicitUndefined directly. To ensure thread safety, restore calling the public RequiresAddingImplicitUndefined, which acquires the lock.

addUndefinedForParameter := declaration != nil && (ast.IsParameter(declaration) /*|| ast.IsJSDocParameterTag(declaration)*/) && b.ch.GetEmitResolver(nil, true).requiresAddingImplicitUndefined(declaration, symbol, b.ctx.enclosingDeclaration)

[weswigham]

I did this for a bunch of other entrypoints, so this tracks, but where is this showing up?

[jakebailey]

It's blocked three PRs from merging so far; the race message is in #1151.