API: add checker methods to get true and false types of a conditional type

[piotrtomiak]

No description provided.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds API surface to retrieve the true/false branch types of a conditional type through the Checker, wiring it through the Go RPC layer and exposing it in both sync and async TypeScript clients.

Changes:

• Exported Checker.GetTrueTypeOfConditionalType / Checker.GetFalseTypeOfConditionalType in Go.
• Added new RPC methods/handlers and proto method registration for both operations.
• Added sync/async TypeScript client methods plus corresponding tests.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
internal/checker/exports.go	Exposes conditional-type branch getters on the public Checker API.
internal/api/session.go	Routes and implements new RPC handlers that resolve a type handle and return the corresponding branch type.
internal/api/proto.go	Registers two new RPC method names and their unmarshallers.
_packages/native-preview/src/api/sync/api.ts	Adds sync TS client methods for conditional-type true/false branches.
_packages/native-preview/src/api/async/api.ts	Adds async TS client methods for conditional-type true/false branches.
_packages/native-preview/test/sync/api.test.ts	Adds sync test coverage validating branch types for a conditional type alias.
_packages/native-preview/test/async/api.test.ts	Adds async test coverage validating branch types for a conditional type alias.

[mrazauskas]

Could you link to #2851, please?

I was suggesting adding .getTrueType() and .getFalseType() to ConditionalType, but anyway this would solve the same problem.

[piotrtomiak]

@mrazauskas - what do you mean by link? In the git commit message?

I was suggesting adding .getTrueType() and .getFalseType() to ConditionalType, but anyway this would solve the same problem.

I am planning to make this change once #4341 is merged, since this requires association between Type and projectId on the API side, which is now missing