Start of work to merge custom nodes into lexical, removing old unused format/indent core logic while extending common block elements where possible.

Continuation to merge and integrate custom & original lexical code for simpler/cleaner result.

Todo

• Merge custom nodes, updating base nodes to use common block node where possible:
  • Heading
  • List
  • List item
  • Quote
  • Table
  • Table cell
  • Table row
• Reorganise/cleanup old custom common node code
• Reorganise existing nodes to new location
• Update testing