[lexical-yjs] Feature: Expose function to get anchor and focus nodes for given user awareness state

[amanharwara]

This PR exposes a getAnchorAndFocusCollabNodesForUserState function extracted from the internal sync cursor functions that allows getting the anchor/focus nodes and offsets when provided a binding and a user state.

We want to implement a "scroll to user cursor" feature, but currently there is no way to get the anchor and focus nodes for a given user as a consumer of Lexical (except for the local, of course).

This also allows for potential custom implementations of collab cursors since the implementation provided in @lexical/yjs is not very customizable.

Screen recording confirming collab cursors work even after the change:

lexical-collab-cursors.mp4

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Name	Status	Preview	Comments	Updated (UTC)
lexical	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Dec 11, 2024 2:48pm
lexical-playground	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Dec 11, 2024 2:48pm

[github-actions]

size-limit report 📦

Path	Size
lexical - cjs	31.18 KB (0%)
lexical - esm	31 KB (0%)
@lexical/rich-text - cjs	40.15 KB (0%)
@lexical/rich-text - esm	32.83 KB (0%)
@lexical/plain-text - cjs	38.79 KB (0%)
@lexical/plain-text - esm	30.15 KB (0%)
@lexical/react - cjs	42 KB (0%)
@lexical/react - esm	34.23 KB (0%)