LFX: Add the file watcher and its test back to KCL

[Siddhi-agg]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• [ ] N
• [x] Y re https://github.com/kcl-lang/kcl/issues/1847

2. What is the scope of this PR (e.g. component or file name):

kcl/kclvm/tools/src/LSP/src/tests.rs kcl/kclvm/tools/src/LSP/src/state.rs

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

• [ ] Affects user behaviors
• [ ] Contains syntax changes
• [ ] Contains variable changes
• [ ] Contains experimental features
• [ ] Performance regression: Consumes more CPU
• [ ] Performance regression: Consumes more Memory
• [ ] Other

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• [ ] N
• [ ] Y

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• [ ] Unit test
• [ ] Integration test
• [ ] Benchmark (add benchmark stats below)
• [ ] Manual test (add detailed scripts or steps below)
• [ ] Other