fix: literal str and join str inner completion

[He1pa]

Remove the special judgment for literal strings during completion, and change the search for the nearest symbol during completion to the symbol one or two characters before the trigger.

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

• N
• Y

fix #1083

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

kclvm/tools/src/LSP/src/completion.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

[coveralls]

Pull Request Test Coverage Report for Build 8077694267

Details

• 9 of 9 (100.0%) changed or added relevant lines in 1 file are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.003%) to 71.939%

---

Files with Coverage Reduction	New Missed Lines	%
kclvm/tools/src/LSP/src/util.rs	3	71.11%

Totals
Change from base Build 8065148886:	0.003%
Covered Lines:	44401
Relevant Lines:	61720

---

💛 - Coveralls

[Peefy]

LGTM