feat: index sign key name reference in the schema body

[Peefy]

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

• N
• Y

Closes #577

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

• kclvm/compiler/src/codegen/llvm/node.rs
• kclvm/runtime/src/value/api.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

feat: index sign alias ref in the schema body

schema TeamSpec[id: str]:
    fullName: str
    name = id
    shortName: str = name

schema TeamMap:
    [n: str]: TeamSpec = TeamSpec(n)  # OK: `n` can be referenced from the index signature key name.

Team = TeamMap {
    a.fullName = "alpha"
    b.fullName = "bravo"
}

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

• test/grammar/schema/index_signature//

6. Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[coveralls]

Pull Request Test Coverage Report for Build 5367505275

• 42 of 65 (64.62%) changed or added relevant lines in 2 files are covered.
• 31 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-19.9%) to 68.096%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
kclvm/compiler/src/codegen/llvm/node.rs	42	44	95.45%
kclvm/runtime/src/value/api.rs	0	21	0.0%

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

Totals
Change from base Build 5311305827:	-19.9%
Covered Lines:	30926
Relevant Lines:	45415

---

💛 - Coveralls

[zong-zhe]

LGTM