test(minifier): add variable collapsing test cases

[DonIsaac]

Add test cases for the variable declaration collapsing AST pass

[DonIsaac]

[!WARNING] This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite. Learn more

• #6227 👈
• #6226
• main

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[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #6227 will not alter performance

_{Comparing don/10-01-test_minifier_add_variable_collapsing_test_cases (3d03f87) with don/10-01-fix_minifier_collapse_variables_when_join_vars_option_is_true (ea896ec)}

Summary

✅ 29 untouched benchmarks

[shulaoda]

It seems that we should not put it separately in a file. See https://github.com/oxc-project/oxc/pull/5912

BTW, I am curious about where these test cases came from. Shouldn't we prioritize copying them from the closure-compiler? See this 🤔