feat(merge): blocks of different types can be merged

[neSpecc]

This PR based on #2564 made by @GuillaumeOnepilot

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Feature

Now it is possible to merge blocks of different types.

If blocks provides the conversionConfig, we use it for merging:

BlockA -> string -> BlockB

blocks-merging.mov

Changes

• requestAnimationFrame removed from BlockEvents@mergeBlocks. It was added because Paragraph was having RAF in merge() method. It was removed by fix(merge): incorrect caret position on merge editor-js/paragraph#86
• normalize() removed as well since it creates issues with caret restoring — nodes text length changes and caret is being set in wrong position. It's better to call normalize() at the tool's merge() method if needed.
• mergeBlocks and areBlocksMergeable logic improved:
  • Target block tool should have the merge() method (be .mergeable)
  • Merging blocks should be the same type
  • or Merging blocks should have the conversionConfig
• In case of using conversion:
  1. We convert blockToMerge data to string
  2. Sanitize string
  3. Convert that string to the target's block data
  4. Call targetBlock.merge()
• Sanitising added to the merging content.
• Cypress updated to fix CI which is broken on all last PRs

[GuillaumeOnepilot]

Thanks for the changes 👍

[gohabereg]

It seems areBlocksMergable can be used here

[neSpecc]

areBlockMergeable is checked before mergeBlocks call. I've written these 2 statements explicitly for clarity: first about same-tool merge, second about merging through the conversion