* Fix the chat context menu removing UTF8 characters causing pure UTF8 character filenames not to display in the menu
* fix: Refactor the function constructNewFileContent using a state switching mechanism, and fix the issue of inaccurate SEARCH-REPLACE delimiters generated by some large models through lookahead processing
* Merge diff.ts with diff2.ts; Mark the original constructNewFileContent as @deprecated.
* Add detailed comments to explain test cases for nested markers
