Mobile: Improve inline search performance in large documents

[personalizedrefrigerator]

Summary

This change improves search performance in large documents by fixing two issues:

1. Fixes an unnecessary state recomputation. Updating the search caused the initial injectedJavaScript to be recomputed. This involved serializing a JSON object that includes the initial editor text. The changes to the injectedJavaScript object then caused other state to update.
2. Fixes an issue with syncing state to the WebView: If 1) the user was typing quickly and 2) IPC to/from the note editor was slow, the search query could reset to older values while typing.

Testing plan

iOS 18.4 simulator, Web:

1. Create a very large note (~100,000 lines).
2. Open the search panel.
3. Search for text known to be present in the note.
4. Press enter and verify that the editor scrolls to one of the matches.
5. Quickly type in the search query box such that the search query is a long string.
6. Verify that the search query updates without briefly reverting to older values.
7. Close and re-open the note.
8. Verify that the editor loads and that the note content is visible.

Web (regression testing):

1. Open a small existing note in the Rich Text editor.
2. Verify that it's possible to 1) open the search bar and 2) search for text known to be in the document.