Expose Checker.getAwaitedType on the unstable API

[Baptiste Jamin (baptistejamin)]

getAwaitedType already exists on the TypeScript 6 checker (ts.TypeChecker.getAwaitedType) and internally in the Go checker, but it is not wired through typescript/unstable. This PR exports it on the JS API so callers can get the type of await expr.

Behavior matches the existing checker:

• unwraps thenables recursively (Promise<string> → string, Promise<Promise<number>> → number)
• returns the input type when it is not thenable
• returns undefined for a circular thenable
• wraps generic Promise<T> as Awaited<T> when needed

This is needed by typescript-eslint (discriminateAnyType, no-unsafe-return) and other tools that still call checker.getAwaitedType.

[Copilot]

Pull request overview

Exposes getAwaitedType through the unstable synchronous and asynchronous TypeScript APIs.

Changes:

• Adds checker and protocol support for awaited-type requests.
• Implements sync and async client methods with nullable results.
• Tests promise unwrapping, non-thenables, nesting, and recursive thenables.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tsc/internal/checker/exports.go	Exports the internal awaited-type operation.
tsc/internal/api/session.go	Handles awaited-type API requests.
tsc/internal/api/proto.go	Registers the new protocol method.
packages/typescript/src/api/proto.generated.ts	Adds generated protocol typing.
packages/typescript/src/api/sync/api.ts	Exposes the synchronous checker method.
packages/typescript/src/api/async/api.ts	Exposes the asynchronous checker method.
packages/typescript/test/sync/api.test.ts	Tests synchronous behavior.
packages/typescript/test/async/api.test.ts	Tests asynchronous behavior.

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[Baptiste Jamin (baptistejamin)]

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