fix: add diagnostic telemetry and user-visible warning for URI handler failures (fixes #655)

[hanhan761]

Summary

The globalUriHandler telemetry showed a 100% error rate. The most likely root cause is URIs being opened without a connectionString query parameter, causing extractAndValidateParams to throw an opaque error with no user-visible feedback.

Changes

• Added diagnostic telemetry to the handler entry point: uriScheme, uriAuthority, uriPathLength, uriQueryLength, uriHasQuery — all non-sensitive, to help identify the actual failure pattern
• Added queryFragmentNonEmpty telemetry in extractAndValidateParams and failureStage in the catch block to pinpoint which step fails
• When connectionString is missing, surfaces a user-visible warning message instead of failing silently with only telemetry:

  "A DocumentDB deep-link was opened without a connection string. Ensure the link includes a connectionString query parameter."

Issue

Fixes #655

Verification

• Single-file change (src/vscodeUriHandler.ts, +18 lines)
• No logic changes to the success path — only telemetry additions and a warning message
• Null-safe: uri.query ?? '' guards against undefined query

[Copilot]

Pull request overview

Note

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

Adds additional telemetry diagnostics and a targeted user-facing warning to improve troubleshooting of VS Code deep-link/URI handling failures.

Changes:

• Record non-sensitive URI metadata (scheme/authority/path/query lengths) into telemetry for debugging.
• Add a failureStage telemetry property in the top-level URI handler error path.
• Show a warning message when a deep-link is missing the required connectionString query parameter.

[tnaum-ms]

Maintainer note (review-driven changes)

On top of the original diagnostics, this branch adds a few review-driven, non-sensitive telemetry properties: errorName capture in the top-level catch (error type only, never the message), parameter counting (known vs unknown query keys) via URLSearchParams, and a connectionStringScheme classifier (mongodb / mongodb+srv / other). No secrets or connection details are logged.

A stray emdash was also removed from a code comment.

Note for reviewers: vscodeUriHandler.ts has heavy vscode/storage dependencies and no unit test; these telemetry-only changes were validated through the full build and test suite.