Block notes: "All notes" button visible when show template is on, even when there are no notes

[hbhalodia]

What?

Closes #73659

Why?

• PR addresses notes sidebar button to show only when adding new note or notes length is greater than 0.

How?

• Updates, showAllNotesSidebar to use notes length and state of note to add the new note.

Testing Instructions

1. Open post/page.
2. Check notes button in plugin sidebar, should not be visibile if no notes.
3. Change to show template mode, it should not show button if no notes.
4. Add notes with both mode, post-only and template-locked, it should show notes panel and when added it should show button to see notes.

Testing Instructions for Keyboard

• None

Screencast

Screen.Recording.2025-12-01.at.12.57.16.PM.mov

[t-hamano]

This issue has been resolved by #74577. I would like to close this PR, but thank you for your efforts!