API: Add declaration property to IndexInfo.

[piotrtomiak]

I've found out one more missing API for WebStorm integration - lack of declaration property on the IndexInfo object.

[Copilot]

Pull request overview

Note

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

Exposes the AST declaration for index signatures through the Go API and surfaces it in the native-preview TypeScript clients.

Changes:

• Added IndexInfo.Declaration() to access the index signature’s declaration node.
• Extended IndexInfoResponse to include an optional declaration node handle and populated it in the session handler.
• Updated native-preview sync/async TS proto + typed APIs to carry and hydrate the new declaration field.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
internal/checker/types.go	Adds a getter for the index signature declaration node.
internal/api/session.go	Includes the declaration node handle in index-info results when available.
internal/api/proto.go	Extends IndexInfoResponse with a declaration field.
_packages/native-preview/src/api/proto.ts	Adds declaration?: string to the TS response shape.
_packages/native-preview/src/api/sync/types.ts	Adds declaration?: NodeHandle to IndexInfo.
_packages/native-preview/src/api/sync/api.ts	Hydrates declaration into a NodeHandle when present.
_packages/native-preview/src/api/async/types.ts	Adds declaration?: NodeHandle to IndexInfo.
_packages/native-preview/src/api/async/api.ts	Hydrates declaration into a NodeHandle when present.