Improve folder selection in file upload dialogs

[digitmaster]

This provides the Bedrock frontend changes for the second feature request in concretecms/concretecms#12083.

Companion PR: concretecms/concretecms#13060.

The folder dropdown in file upload dialogs is replaced with a scalable folder picker that provides:

• A lazily loaded folder tree for browsing.
• Remote folder search displaying up to 50 matching folders. When additional matches exist, the picker shows "More folders found. Refine your search." so users can narrow the query and retrieve the desired folder.
• A clear indication of the current upload destination.
• An improved folder creation flow that shows the selected parent path, focuses the name field, allows the operation to be cancelled, and automatically selects the newly created folder.
• Permission-aware folder selection.
• Folder name validation matching the existing 255-character database limit.

The folder search queries only folder tree nodes and does not load files or file versions, allowing the picker to remain usable with large file libraries.

Testing

• Tested all three file picker instances on the Bookmark Icons dashboard page.
• Tested folder browsing, remote search and synchronization between search results and the tree.
• Tested folder creation, cancellation, focus handling and automatic selection.
• Tested names at the 255-character boundary and rejection of longer or malformed values.
• Ran Bedrock StandardX checks.