issue #7456: TextComposite toolbar with find/replace and plugin SPI

[mattcasters]

Summary

Implements in-editor search for multi-line SQL/script/text fields (issue #7456), and opens the same surface for plugins:

• Toolbar on TextComposite (same SPI model as TableView): undo/redo, cut/copy/paste, select all, find, find/replace
• Find/replace dialog with Ctrl+F / Ctrl+H and context menu
• styleType constructor parameter so toolbar filters see SQL/JSON/… at build time (filters run mid-construction)
• Plugin contribution via @GuiToolbarElement + @GuiToolbarElementFilter on TextComposite.ID_TOOLBAR
• Sample JSON pretty-print button in the JSON transform plugin
• Developer documentation: GUI plugins and toolbars
• Config option to show/hide the text editor toolbar

Notes for reviewers

• Prefer getStyleType() over instanceof specialized subclasses (Hop Web stand-ins).
• @GuiToolbarElementFilter runs during host construction: use constructor styleType only; check isEditable() / content in the action method.
• Runtime: TextFindSupport unit tests; compile verified for ui and affected plugins.

Test plan

• Open Table Input / Exec SQL / SQL Editor: toolbar visible; Ctrl+F finds text; Ctrl+H replace works
• Mongo/JSON fields (styleType JSON): format-JSON toolbar button appears; pretty-prints valid JSON; invalid JSON shows error dialog
• Read-only log panels: find available; edit actions disabled where appropriate
• Configuration → show text editor toolbar off: toolbars hidden
• Hop Web: SQL fields use StyledTextComp with STYLE_TYPE_SQL; toolbar/find still work

Fixes #7456