fix: fix empty identifier expr position

[He1pa]

fix empty identifier expr postion and completion for literal str in lsp

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

• N
• Y fix [Enhancement][Track] KCL VSCode IDE extension and lsp enhancement #524

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

parser, lsp

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 5442924724

• 64 of 64 (100.0%) changed or added relevant lines in 3 files are covered.
• 31 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-19.9%) to 68.061%

---

Files with Coverage Reduction	New Missed Lines	%
compiler_base/session/src/lib.rs	31	50.0%

Totals
Change from base Build 5442553920:	-19.9%
Covered Lines:	30929
Relevant Lines:	45443

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💛 - Coveralls

[Peefy]

LGTM