Portable Text Editor Input migrated to Sanity UI

We have now migrated the Portable Text (PT) editor in the Sanity Studio to use Sanity UI. This marks the completion of the migration of the entire Studio to @sanity/ui.

In addition to the migration:

• Generally improved stability and performance of the PT editor.
• Added a new affordance for editing/removing text annotations. This will make it easier to e.g. edit link details.
• Fixed a bug where undo/redo history was not maintained in memory when collapsing/expanding the editor.

• Allows plan selection with sanity init --project-plan <plan>
• Improves usability of ValidationError by making cloneWithMessage optional