Fix stack overflow in getExplicitTypeOfSymbol() for self-referential for...of

[johnfav03]

Fixes an issue uncovered in #4532 (comment); with a self-referential type whose iterable is the loop variable itself (for (const a of a)), getExplicitTypeOfSymbol() faces unbound recursion. This PR fixes that by keeping a set in the checker keyed by the symbol, which guards the function with AddIfAbsent and otherwise removes the symbol from the set at the end of the function.

[Copilot]

Pull request overview

Fixes an infinite recursion/stack overflow in the Go checker’s getExplicitTypeOfSymbol() when analyzing self-referential for...of constructs (e.g. for (const a of a)), by adding a per-checker recursion guard keyed by symbol and validating the behavior with a new compiler regression test and baselines.

Changes:

• Added a Checker.resolvingExplicitTypeOfSymbol set and used it to short-circuit recursive re-entry in getExplicitTypeOfSymbol().
• Added a regression compiler test covering for (const a of a) with subsequent usage patterns that previously triggered unbounded recursion.
• Checked in new reference baselines for diagnostics, emit, symbols, and types for the new test.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/checker/checker.go	Adds resolvingExplicitTypeOfSymbol to Checker state for recursion guarding.
internal/checker/flow.go	Uses the new set to prevent unbounded recursion in getExplicitTypeOfSymbol().
testdata/tests/cases/compiler/forOfSelfReferentialDottedName.ts	New regression test reproducing the self-referential for...of scenario.
testdata/baselines/reference/compiler/forOfSelfReferentialDottedName.errors.txt	Expected diagnostics baseline for the new regression test.
testdata/baselines/reference/compiler/forOfSelfReferentialDottedName.js	Expected JS emit baseline for the new regression test.
testdata/baselines/reference/compiler/forOfSelfReferentialDottedName.symbols	Expected symbols baseline for the new regression test.
testdata/baselines/reference/compiler/forOfSelfReferentialDottedName.types	Expected types baseline for the new regression test.