Bug: Forward deletion of CollapsibleContainerNode inconsistent with backwards deletion

[etrepum]

Lexical version: v0.24.0

Steps To Reproduce

example doc

See e2e selection test 'Can delete forward a Collapsible' that encodes this behavior.

1. Position the caret after the right arrow (there needs to be some inline content in the paragraph above, otherwise the empty paragraph gets deleted)
2. Press option-delete for forward delete

When #7155 was implemented to make decorators and elements with shadow roots behave correctly, a workaround was implemented to preserve the behavior encoded by this test.

#7155 (comment)_

The current behavior

The node's content gets spliced into the document

The expected behavior

The collapsible gets deleted

Impact of fix

Consistency goes up, code size goes down