Prepare action for public rust support

[redsun82]

This makes it so that once the codeql that is being used by the action supports Rust extraction out of the box we skip all the experimental handling code.

Functionally (considering the feature flag will also be switched at that moment), this will primarily result in skipping to print
Experimental rust analysis enabled in that case. Once the feature flag is switched, we can clean up this code (though not remove it entirely to ensure backward compatibility).

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Confirm the readme has been updated if necessary.
• Confirm the changelog has been updated if necessary.

[Copilot]

Pull Request Overview

This PR updates the Rust support logic to only enable the experimental CodeQL feature flag when the installed CodeQL version lacks built-in Rust support.

• Add a codeql.resolveLanguages() check before exporting CODEQL_ENABLE_EXPERIMENTAL_FEATURES for Rust
• Mirror the updated logic and comment in both the TypeScript source and compiled JavaScript

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/init-action.ts	Conditionally set experimental Rust feature flag based on detected CodeQL support
lib/init-action.js	Apply the same conditional check and updated comment in the built JS