[Breaking Change][lexical][lexical-utils]: Bug Fix: Handle canBeEmpty in $splitNodes

[etrepum]

Breaking Change

Previously $insertNodeToNearestRoot could create empty ElementNode when splitting the current node, now it respects canBeEmpty() and will not split in those cases.

Description

This change makes $insertNodeToNearestRoot to respect the canBeEmpty() method of the nodes it is splitting and provides infrastructure to better control splitting (SplitAtPointCaretNextOptions, $insertNodeToNearestRootAtCaret, $splitAtPointCaretNext).

New lexical APIs:

• $splitAtPointCaretNext - a lower-level API to split at the given caret exactly once (not recursive) with full control over how that happens
• $getCollapsedCaretRange(pointCaret) - convenience for $getCaretRange(pointCaret, pointCaret) to reduce redundant code

New @lexical/utils API:

• $insertNodeToNearestRootAtCaret - lower-level API that does $insertNodeToNearestRoot recursive split and then insert without the quirks and selection changes (those happen in the $insertNodeToNearestRoot function).

I'm not very fond of the manner in which nodes are split (the empty splits are a bit awkward especially when not a ParagraphNode), but this doesn't break backwards compatibility in any case that we test and this function is only used in the playground and the implementation of commands that can be easily overridden (e.g. INSERT_HORIZONTAL_RULE_COMMAND). Now that the lower-level functions are exposed, people can control how this works for better UX.

Closes #6849

Test plan

All existing e2e tests pass, new ListNode split test

Before

Splitting an empty ListItemNode creates a broken list:

<ul class="PlaygroundEditorTheme__ul"></ul>
<hr>
<ul class="PlaygroundEditorTheme__ul">
  <li value="1" class="PlaygroundEditorTheme__listItem"></li>
</ul>

After

Splitting an empty ListItemNode creates a complete second list:

<ul class="PlaygroundEditorTheme__ul">
  <li value="1" class="PlaygroundEditorTheme__listItem"></li>
</ul>
<hr>
<ul class="PlaygroundEditorTheme__ul">
  <li value="1" class="PlaygroundEditorTheme__listItem"></li>
</ul>

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Name	Status	Preview	Comments	Updated (UTC)
lexical	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Mar 17, 2025 7:41pm
lexical-playground	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Mar 17, 2025 7:41pm

[etrepum]

DecoratorNode are inline by default but some of these tests were inserting it directly into the root. I added this to make that reasonable.

[etrepum]

/cc @ivailop7