RFR: 8373936: RichEditorDemoApp enhancements [v4]

[Andy Goryachev]

> The goal of this work is to deliver a sufficiently complete implementation of an editor application based on the RichTextArea that users can adopt as is or use as, or use it as a foundation for a more complex editor.
> 
> Improvements include:
> - syncing the toolbar with current character attributes
> - improved toolbar behavior in regards to character attributes, utilizing the new 'insertStyles' property [JDK-8374035](https://bugs.openjdk.org/browse/JDK-8374035)
> - paragraph format dialog, with the associated toolbar button and the main menu item
> 
> <img width="676" height="678" alt="Screenshot 2026-01-15 at 12 01 44" src="https://github.com/user-attachments/assets/9c96e4d2-21f3-43d2-b009-01d6887747f8" />
> 
> Test case related to [JDK-8374035](https://bugs.openjdk.org/browse/JDK-8374035):
> - type something
> - place cursor at the middle of the typed text and hit command-B or ctrl-B on Win/Linux
> - notice how the formatting toolbar highlights [b] button indicating that the style for next character to be inserted has changed to bold
> - type something and confirm that inserted text is bold
> the new style is captured only in the toolbar UI, so clicking on some other part of the text reverts the bold button to the unselected state.

Andy Goryachev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 37 commits:

 - Merge branch 'master' into 8373936.editor
 - actions
 - Merge branch 'master' into 8373936.editor
 - Merge branch 'master' into 8373936.editor
 - Merge branch 'master' into 8373936.editor
 - whitespace
 - whitespace
 - Merge branch '8374035.insert.styles' into 8373936.editor
 - 2026
 - Merge branch 'master' into 8374035.insert.styles
 - ... and 27 more: https://git.openjdk.org/jfx/compare/422d3a95...df6dbb17

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Changes: https://git.openjdk.org/jfx/pull/2026/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=2026&range=03
  Stats: 1323 lines in 12 files changed: 846 ins; 349 del; 128 mod
  Patch: https://git.openjdk.org/jfx/pull/2026.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/2026/head:pull/2026

PR: https://git.openjdk.org/jfx/pull/2026