feat: lsp completion of pkg, var and schema attr

[He1pa]

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

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

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

LSP
Scope

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

feat: lsp completion of pkg, var and schema attr

• 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 5653653220

• 243 of 260 (93.46%) changed or added relevant lines in 9 files are covered.
• 26 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-19.4%) to 68.547%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
kclvm/tools/src/LSP/src/document_symbol.rs	0	1	0.0%
kclvm/tools/src/LSP/src/goto_def.rs	3	4	75.0%
kclvm/tools/src/LSP/src/util.rs	9	11	81.82%
kclvm/sema/src/resolver/scope.rs	21	24	87.5%
kclvm/tools/src/LSP/src/completion.rs	100	110	90.91%

Files with Coverage Reduction	New Missed Lines	%
compiler_base/session/src/lib.rs	26	58.06%

Totals
Change from base Build 5644626118:	-19.4%
Covered Lines:	31555
Relevant Lines:	46034

---

💛 - Coveralls

[Peefy]

LGTM