[WIP] #3067 statement warnings api

[noeldevelops]

🚧 WIP

Summary of Changes

• Display statement warnings that are returned with new API
• Preserves legacy format for statement warnings inside of Details, but prefers warnings api when available
• Rearranges the way error, info, warnings details are surfaced in the Statement Results Viewer header section

Click-testing instructions

Changes are visible in the VS Code Flink Statement Results viewer when there are Statement Details, Errors, or Warnings

To test, check this branch out locally and:

1. Run a Flink statement that you know will produce a warning or error
2. Stop a statement that is running to see the Info message "This statement was stopped manually."
3. OR, add dummy data in flink-statement-results.ts file -- set this.hasWarnings to true & add an array of mocks e.g.

 this.formattedWarnings = this.derive(() => {
      const mockWarnings = [ {
          severity: "LOW",
          message: "This is a low severity warning for testing purposes.",
          reason: "LOW_SEVERITY_TEST",
          createdAt: "2025-11-14T15:00:00Z",
          isCritical: false,
        }, ...

Optional: Any additional details or context that should be provided?

• Feature flag for the new warnings API is not flipped yet; we'll stay backward compatible for the time being

Pull request checklist

Please check if your PR fulfills the following (if applicable):

Tests

• Added new
• Updated existing
• Deleted existing

Release notes

• Does anything in this PR need to be mentioned in the user-facing CHANGELOG?