Add SVG cursors for all cursor types (#1416)

Fixes #1410 

This PR adds custom SVGs for all cursor types.
This will unblock some upcoming collaboration features!

It also adds some basic debugging for custom cursors.

![2023-05-19 at 11 02 57 - Coffee
Shrimp](https://github.com/tldraw/tldraw/assets/15892272/dbc84d04-604f-43e5-acd2-69df956e5784)

It uses custom cursors for any shape-related UI, like links.

![2023-05-19 at 11 07 04 - Amaranth
Aphid](https://github.com/tldraw/tldraw/assets/15892272/7eb25f6a-0552-47bd-b2b9-f6c3dc2fca70)

But it sticks with the default browser cursors for the non-canvas UI.

![2023-05-23 at 15 06 29 - Apricot
Bovid](https://github.com/tldraw/tldraw/assets/15892272/2fe35afb-095a-4454-a6c3-aa8337b71506)

### Change Type

- [x] `minor`

### Test Plan

1. Enable debug mode.
2. From the debug menu, enable "Debug cursors".
3. Hover the cursor over the shapes that appear.
4. Check that the cursor appears correctly over each one.
5. (Don't forget to turn off "Debug cursors" after use).

### Release Notes

- Added consistent custom cursors.

---------

Co-authored-by: Steve Ruiz <steveruizok@gmail.com>

packages/editor/src/lib/utils/debug-flags.ts

@@ -23,6 +23,7 @@ export const debugFlags = {
 	peopleMenu: createDebugValue('tldrawPeopleMenu', false),
 	logMessages: createDebugValue('tldrawUiLog', []),
 	resetConnectionEveryPing: createDebugValue('tldrawResetConnectionEveryPing', false),
+	debugCursors: createDebugValue('tldrawDebugCursors', false),
 }
 
 declare global {