Complete port of TS PR #61668: revert #57403 remnants missing from Go port

[Copilot]

The Go port of TypeScript PR #61668 (PR #1795) only ported the new createOuterReturnMapper machinery but omitted the revert of TS PR #57403 that the original PR also performed. This leaves the Go checker with dead/conflicting code that was supposed to be removed.

Missing changes now ported

• Remove isTupleOfSelf (inference.go): Discarded the early-exit for inferences of the form A → [A[0]]. The new createOuterReturnMapper approach handles circular inference prevention more generally.

• Remove getImplementationSignature / SignatureKeyImplementation (checker.go): Eliminated the candidate-cloning path that was triggered when resolving a call from inside the called function's own body. No longer needed with the revised contextual type instantiation strategy.

• Remove instantiateTypes wrapping around inferTypeArguments (checker.go, chooseOverload): Both the first-pass (nonFixingMapper) and second-pass (mapper) wrappings were TS PR #57403 additions and are now dropped, so inferTypeArguments results are used directly.

• Remove inferenceContext parameter from isSignatureApplicable (checker.go): The parameter was only used to instantiate argument types via nonFixingMapper before assignability checks—another TS PR #57403 artifact. Simplified to always use the plain (possibly regularized) argument type.

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[Copilot]

Pull request overview

This PR completes the Go port of TypeScript PR #61668 by including the missing “revert PR #57403” cleanups in the checker, removing now-obsolete inference and overload-resolution machinery that conflicts with the newer createOuterReturnMapper approach.

Changes:

• Removes the isTupleOfSelf early-exit inference heuristic from inferFromTypes.
• Removes the “implementation signature” cloning path (getImplementationSignature / SignatureKeyImplementation) used when resolving calls inside a function’s own body.
• Simplifies overload applicability/type inference flow by dropping instantiateTypes(...) wrapping around inferTypeArguments(...), and removing the inferenceContext parameter from isSignatureApplicable.

Reviewed changes

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

File	Description
internal/checker/inference.go	Removes isTupleOfSelf and its use in inference candidate handling.
internal/checker/checker.go	Removes implementation-signature caching/cloning and simplifies overload applicability and inference plumbing to match upstream revert.

[ahejlsberg]

I have manually verified that this adds the missing parts of TS PR #61668.