Fix: Record used module

[He1pa]

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

• N
• Y fix [Enhancement] Record whether the module has been used in symbol table(Scope) #132

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

sema/resolver/var.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

Fix bug in resolve_var(). When enter child scope, e.g., in a schema scope, cant find module object.
It should be recursively search whole scope to lookup module object, not the current scope.element.

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

6. Release note

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

None

[zong-zhe]

LGTM

[coveralls]

Pull Request Test Coverage Report for Build 2872278828

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.6%) to 58.995%

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Totals
Change from base Build 2872238247:	-0.6%
Covered Lines:	21365
Relevant Lines:	36215

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💛 - Coveralls

[Peefy]

LGTM

[zong-zhe]

LGTM