Verify PR #59661 implementation is already ported

[Copilot]

This PR confirms that the changes from TypeScript PR #59661 ("Report implicit any error when widening null/undefined in presence of generic contextual signatures") have already been successfully ported to the Go codebase.

Analysis Summary

The investigation revealed that all key components from the original TypeScript PR are already implemented:

✅ Core Logic Changes

• shouldReportErrorsFromWideningWithContextualSignature() function exists in internal/checker/checker.go
• reportErrorsFromWidening() contains the updated conditional logic
• Logic correctly handles generic return types in contextual signatures

✅ Diagnostic Message Updates

• Message TS7025 updated to remove "because it does not yield any values" text
• Located in internal/diagnostics/diagnostics_generated.go

✅ Test Coverage

• All test cases from the original PR exist in the submodule
• Baseline files show correct error reporting for all scenarios
• Key Promise.catch/then cases properly caught (fixes Promise.catch null vs null as null microsoft/TypeScript#44913)

✅ Behavior Verification

Tested the Go implementation against the exact test cases from the TypeScript PR:

// These correctly report TS7011 implicit any errors:
declare function f1<T>(cb: () => T): void;
f1(() => null);

Promise.resolve().catch(e => null);
Promise.resolve().then(v => null);

The Go compiler produces identical output to the official TypeScript compiler, confirming the port is complete and correct.

No Changes Required

Since the implementation is already complete and working correctly, no code changes were made to the repository.

Fixes #18.

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