Refactor: clean blockcontainer (#1137)

* extract updateBlockCommand

* Extracted remaining commands

* extract keyboard shortcuts

* move directory

* remove createblockcommand

* Added merge/split tests

* Updated snapshots

* Added update block tests and unified test setup

* Added test cases for reverting props

* Added additional test cases for changing content type

* remove "nested" insert option

* Split remaining commands & cleaned up

* Added `getNearestBlockContainerPos`

* Refactored `getBlockInfoFromPos`

* Rewrote `splitBlockCommand`

* Added text cursor position tests

* Fixed lint issue

* fix lint

* Fixed `splitBlock` selection

* Small fix

* Added unit tests to check selection setting

* simplify splitblocks

* Fixed selection in `splitBlock` tests

* wip: deprecate getBlockInfoFromPos

* finish cleanup

* Fixed `mergeBlocks` edge cases

* fix build

* clean nodeconversions

* Implemented PR feedback

* Finished review and remaining changes

* Fixed bug in `insertOrUpdateBlock`

* Removed log

* Tiny changes

* Fixed merge/delete behaviour on Backspace

---------

Co-authored-by: matthewlipski <matthewlipski@gmail.com>
Co-authored-by: Matthew Lipski <50169049+matthewlipski@users.noreply.github.com>

Author: YousefED

docs/pages/docs/editor-api/manipulating-blocks.mdx

@@ -115,7 +115,7 @@ Use `insertBlocks` to insert new blocks into the document:
 insertBlocks(
   blocksToInsert: PartialBlock[],
   referenceBlock: BlockIdentifier,
-  placement: "before" | "after" | "nested" = "before"
+  placement: "before" | "after" = "before"
 ): void;
 
 // Usage
@@ -126,7 +126,7 @@ editor.insertBlocks([{type: "paragraph", content: "Hello World"}], referenceBloc
 
 `referenceBlock:` An [identifier](/docs/editor-api/manipulating-blocks#block-identifiers) for an existing block, at which the new blocks should be inserted.
 
-`placement:` Whether the blocks should be inserted just before, just after, or nested inside the `referenceBlock`. Inserts the blocks at the start of the existing block's children if `"nested"` is used.
+`placement:` Whether the blocks should be inserted just before or just after the `referenceBlock`.
 
 If a block's `id` is undefined, BlockNote generates one automatically.