API: cache SourceFile text to heavily improve performance

[piotrtomiak]

When using getTokenPosOfNode on various nodes, each time SourceFile text is required causing huge performance issues. This is a minimal change to improve performance in such cases. I wonder though, whether such a cache shouldn't be on each Node. CC @andrewbranch

[Copilot]

Pull request overview

This PR improves performance in the native-preview remote AST layer by caching SourceFile.text so repeated calls (e.g. from getTokenPosOfNode → getStart/getText) don’t repeatedly decode the source text from the string table.

Changes:

• Add a __cachedText field and cache logic to the generated RemoteNode.text getter for SyntaxKind.SourceFile.
• Update the generator (_scripts/generate-encoder.ts) so the caching logic is consistently produced in node.generated.ts.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
_scripts/generate-encoder.ts	Updates code generation for RemoteNode.text to include a SourceFile text cache.
_packages/native-preview/src/api/node/node.generated.ts	Generated output reflecting the new SourceFile text cache in RemoteNode.text.

[andrewbranch]

This is a good optimization—could you put the cache on RemoteSourceFile instead of RemoteNode and override get text() there?