Upgrade blocknote dependencies from 0.31.1 to 0.47.0. (#18207)

This PR pgrades all BlockNote packages (@blocknote/core,
@blocknote/react, @blocknote/mantine, @blocknote/server-util,
@blocknote/xl-docx-exporter, @blocknote/xl-pdf-exporter) to 0.47.0 and
adapts the codebase to the new API.

### Changes
- Dependency upgrades: Bumped all BlockNote packages to 0.47.0, added
required Mantine v8 peer dependencies, removed unnecessary prosemirror
resolutions
- Formatting toolbar: Replaced the manual reimplementation of
FormattingToolbarController (which handled visibility, positioning,
portal rendering, text-alignment-based placement, and a
dangerouslySetInnerHTML transition trick) with BlockNote's built-in
FormattingToolbarController. The toolbar buttons themselves are
unchanged.
- Side menu: Replaced manual drag handle menu positioning and rendering
(DashboardBlockDragHandleMenu, DashboardBlockColorPicker, and their
floating configs) with BlockNote's built-in SideMenuController,
DragHandleButton, and DragHandleMenu components. Deleted 4 files that
became dead code.
- Extension API migration: Replaced deprecated editor.suggestionMenus
and editor.formattingToolbar APIs with the new extension system
(SuggestionMenu, useExtensionState, editor.getExtension())
- Slash menu fixes: Filtered out BlockNote's new default "File" item
(added in 0.47) to avoid duplicates with our custom one; added icon
mappings for new block types (Toggle List, Divider, Toggle Headings,
Headings 4-6)
- Server-side: Switched @blocknote/server-util to dynamic import() to
handle ESM-only transitive dependencies in CJS context

package.json

@@ -201,8 +201,6 @@
     "type-fest": "4.10.1",
     "typescript": "5.9.2",
     "graphql-redis-subscriptions/ioredis": "^5.6.0",
-    "prosemirror-view": "1.40.0",
-    "prosemirror-transform": "1.10.4",
     "@lingui/core": "5.1.2",
     "@types/qs": "6.9.16"
   },