feat(dedent): add dedent function to remove common indentation

[KimKyuHoi]

Summary

This PR adds a dedent function that removes the common leading indentation from multi-line strings.

Closes #842

TC39 String.dedent Proposal (Stage 2)

This implementation follows the TC39 String.dedent proposal specification:

TC39 Spec	Supported
Tagged template literal	✅
Tag composition (dedent(otherTag)...``)	✅
Remove opening/closing empty lines	✅
Calculate common indentation	✅
Preserve relative indentation	✅

Additional Feature (Beyond TC39)

In addition to the TC39 spec, this implementation also supports regular function calls:

// TC39 spec only defines tagged template usage
dedent`
  hello
  world
`;
// We also support regular function call for convenience
dedent("  hello\n  world");

Usage

import { dedent } from 'es-toolkit/string';

// 1. Tagged template literal (TC39)
const code = dedent`
  function hello() {
    console.log('world');
  }
`;
// → "function hello() {\n  console.log('world');\n}"

// 2. Regular function (additional)
dedent("  line 1\n    line 2");
// → "line 1\n  line 2"

// 3. Tag composition (TC39)
const html = (strings, ...values) => strings.join('');
dedent(html)`
  <div>
    <span>Hello</span>
  </div>
`;

References

• TC39 Proposal: https://github.com/tc39/proposal-string-dedent
• Issue: feature: dedent #842

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Project	Deployment	Review	Updated (UTC)
es-toolkit	Error		Jan 23, 2026 7:09am

[KimKyuHoi]

@raon0211 @dayongkr
Hello guys!
if you have time, would you be able to do a code review? Thanks!