feat: api list_variables supports get variables from multi-files

[zong-zhe]

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

• N
• Y

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

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

[Peefy]

Suggested change

	pub fn list_variables(files: Vec<&str>, specs: Vec<String>) -> Result<ListVariablesResult> {
	pub fn list_variables(files: Vec<String>, specs: Vec<String>) -> Result<ListVariablesResult> {

[Peefy]

Remove un-used code.

[Peefy]

Just use &[String] or Vec<String> instead of Vec<&str>

[coveralls]

Pull Request Test Coverage Report for Build 9347790842

Details

• 73 of 73 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 71.035%

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Totals
Change from base Build 9316725699:	0.04%
Covered Lines:	54606
Relevant Lines:	76872

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💛 - Coveralls