[Editor] Add ux-editor with CKEditor, EditorJS and GrapesJS bridges

[makraz]

Q	A
Bug fix?	no
New feature?	yes
Deprecations?	no
Documentation?	yes
Issues	—
License	MIT

symfony/ux-editor adds a single Symfony form field (EditorType) on top of
multiple content-authoring editors — WYSIWYG, block and page-builder — behind
one consistent API.

The core package is editor-agnostic and provides:

• a polymorphic content model: EditorContentInterface with HtmlContent,
  BlockContent and PageContent, plus an EditorContentFormat enum;
• EditorType form abstraction with data transformers;
• Doctrine custom types (editor_html, editor_blocks, editor_page);
• a signed upload pipeline (EditorUploadController, SignedUploadUrlGenerator,
  EditorUploadHandlerInterface, local handler + registry);
• a ux_editor_render Twig function (HTML sanitized, blocks via registry, page
  rendered in a sandboxed iframe);
• a LiveEditor trait for debounced autosave with LiveComponent;
• a debug:ux-editor console command and a WebProfiler data collector.

Concrete editors plug in through BridgeInterface + BridgeRegistry. This PR
also includes three bridges as separate composer + npm sub-packages:

• symfony/ux-editor-ckeditor — CKEditor 5 (WYSIWYG family)
• symfony/ux-editor-editorjs — EditorJS (block family)
• symfony/ux-editor-grapesjs — GrapesJS (page-builder family)

PHP and JS test suites are included and passing. Documentation lives in
src/Editor/doc/.

[github-actions]

📊 Packages dist files size difference

Thanks for the PR! Here is the difference in size of the packages dist files between the base branch and the PR.
Please review the changes and make sure they are expected.

File	Before (Size / Gzip)	After (Size / Gzip)
Editor
content/EditorContent.d.ts	Added	412 B / 246 B
content/EditorContent.js	Added	402 B / 230 B
controller-BoYyK5_A.js	Added	3.4 kB / 1.2 kB
controller.d.ts	Added	1.25 kB / 508 B
controller.js	Added	111 B / 109 B
format/block_controller.d.ts	Added	446 B / 277 B
format/block_controller.js	Added	249 B / 191 B
format/page_builder_controller.d.ts	Added	409 B / 257 B
format/page_builder_controller.js	Added	368 B / 238 B
format/wysiwyg_controller.d.ts	Added	387 B / 251 B
format/wysiwyg_controller.js	Added	494 B / 317 B
live/live-editor.d.ts	Added	262 B / 206 B
live/live-editor.js	Added	541 B / 298 B
upload/SignedUploadClient.d.ts	Added	421 B / 255 B
upload/SignedUploadClient.js	Added	684 B / 403 B
Editor (Bridge CKEditor)
controller.d.ts	Added	511 B / 306 B
controller.js	Added	1.25 kB / 559 B
Editor (Bridge EditorJS)
controller.d.ts	Added	451 B / 286 B
controller.js	Added	1.57 kB / 679 B
tool-registry.d.ts	Added	151 B / 159 B
tool-registry.js	Added	153 B / 149 B
Editor (Bridge GrapesJS)
controller.d.ts	Added	518 B / 317 B
controller.js	Added	2.16 kB / 743 B