feat(string/dedent): add dedent function for removing common leading whitespace

[sukvvon]

Summary

• Add dedent function that removes common leading whitespace from multi-line strings
• Supports both regular function calls and tagged template literals
• Normalizes CRLF to LF, strips leading/trailing empty lines, preserves relative indentation
• 100% test coverage (15 test cases including edge cases)
• Docs in all 4 languages (en, ko, ja, zh_hans)

Closes #842

Test Plan

• Basic whitespace removal
• Relative indentation preservation
• Tagged template literal with interpolations
• Empty lines, single line, empty string
• Tab indentation, mixed indentation levels
• Windows line endings (CRLF)
• All-empty-line input
• 100% code coverage
• Full test suite passes (4346 tests)

[vercel]

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Project	Deployment	Actions	Updated (UTC)
es-toolkit	Ready	Preview, Comment	Apr 3, 2026 3:14am

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.97%. Comparing base (cd553ee) to head (1adf7ab).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1679   +/-   ##
=======================================
  Coverage   99.97%   99.97%           
=======================================
  Files         497      498    +1     
  Lines        4662     4702   +40     
  Branches     1348     1358   +10     
=======================================
+ Hits         4661     4701   +40     
  Misses          1        1           

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