PanelHeaderMenuTrigger: Store clickCoordinates in a ref instead of state

[ashharrison90]

What is this feature?

• prereq for Chore: Upgrade to react 18 #64428
• rewrites PanelHeaderMenuTrigger code to correctly detect click vs. drag behaviour in react 18
  • the main difference here is storing the initial click coordinates in a ref instead of state.
  • probably due to batched updates in react 18, the state wasn't updated between mouseDown and onClick. using a ref ensures it's always up-to-date.

Why do we need this feature?

• so this code works properly in react 18

Who is this feature for?

• everyone!

Which issue(s) does this PR fix?:

Fixes #

Special notes for your reviewer:

Please check that:

• It works as expected from a user's perspective.
• If this is a pre-GA feature, it is behind a feature toggle.
• The docs are updated, and if this is a notable improvement, it's added to our What's New doc.
• There are no known compatibility issues with older supported versions of Grafana, or plugins.
• It passes the Hosted Grafana feature readiness review for observability, scalability, performance, and security.

[github-advanced-security]

You have successfully added a new CodeQL configuration .github/workflows/pr-codeql-analysis-javascript.yml:analyze. As part of the setup process, we have scanned this repository and found 27 existing alerts. Please check the repository Security tab to see all alerts.

[grafanabot]

This pull request was removed from the 9.5.0 milestone because 9.5.0 is currently being released.

[dprokop]

Works as expected.