Remove helpers / extraneous API methods. (#1745)

This PR removes several extraneous computed values from the editor. It
adds some silly instance state onto the instance state record and
unifies a few methods which were inconsistent. This is fit and finish
work 🧽

## Computed Values

In general, where once we had a getter and setter for `isBlahMode`,
which really masked either an `_isBlahMode` atom on the editor or
`instanceState.isBlahMode`, these are merged into `instanceState`; they
can be accessed / updated via `editor.instanceState` /
`editor.updateInstanceState`.

## tldraw select tool specific things

This PR also removes some tldraw specific state checks and creates new
component overrides to allow us to include them in tldraw/tldraw.

### Change Type

- [x] `major` — Breaking change

### Test Plan

- [x] Unit Tests
- [x] End to end tests

### Release Notes

- [tldraw] rename `useReadonly` to `useReadOnly`
- [editor] remove `Editor.isDarkMode`
- [editor] remove `Editor.isChangingStyle`
- [editor] remove `Editor.isCoarsePointer`
- [editor] remove `Editor.isDarkMode`
- [editor] remove `Editor.isFocused`
- [editor] remove `Editor.isGridMode`
- [editor] remove `Editor.isPenMode`
- [editor] remove `Editor.isReadOnly`
- [editor] remove `Editor.isSnapMode`
- [editor] remove `Editor.isToolLocked`
- [editor] remove `Editor.locale`
- [editor] rename `Editor.pageState` to `Editor.currentPageState`
- [editor] add `Editor.pageStates`
- [editor] add `Editor.setErasingIds`
- [editor] add `Editor.setEditingId`
- [editor] add several new component overrides

packages/editor/src/lib/components/default-components/DefaultHandle.tsx

@@ -2,6 +2,7 @@ import { TLHandle, TLShapeId } from '@tldraw/tlschema'
 import classNames from 'classnames'
 import { ComponentType } from 'react'
 
+/** @public */
 export type TLHandleComponent = ComponentType<{
 	shapeId: TLShapeId
 	handle: TLHandle