Add support for formatting relative times

[connor-baer]

Purpose

The Intl.RelativeTimeFormat object enables language-sensitive relative time formatting, e.g. "1 day ago" or "in 5 months". It's widely supported in browsers, with only Safari lagging behind.

Approach and changes

• Added formatRelativeTime, formatRelativeTimeToParts, resolveRelativeTimeFormat, and isRelativeTimeFormatSupported

Definition of done

• Development completed
• Reviewers assigned
• Unit and integration tests
• Meets minimum browser support
• Meets accessibility requirements

[changeset-bot]

🦋 Changeset detected

Latest commit: c33384d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sumup-oss/intl	Minor

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[codecov]

Codecov Report

Attention: Patch coverage is 97.05882% with 3 lines in your changes missing coverage. Please review.

Project coverage is 94.00%. Comparing base (8c2eefd) to head (ee024f9).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lib/relative-time-format/intl.ts	81.81%	2 Missing ⚠️
src/lib/relative-time-format/index.ts	98.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #286      +/-   ##
==========================================
+ Coverage   93.56%   94.00%   +0.43%     
==========================================
  Files          16       19       +3     
  Lines         715      817     +102     
  Branches       97      124      +27     
==========================================
+ Hits          669      768      +99     
- Misses         44       47       +3     
  Partials        2        2              

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