[ISSUE-237] Add a function to retrieve all supported locales in Jiffy

[jama5262]

What does this PR do?

Add a function to retrieve all supported locales in Jiffy

Issue Reference

Fixes #237

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Maintenance change (non-breaking change such as upgrading a dependency, refactoring, or making a lint fix)
• [ ] Documentation update
• [ ] Breaking change (a fix or feature that would cause existing functionality to change)

Screenshots

If applicable, add screenshots to help explain your problem.

Checklist

• [x] Wrote additional tests, if needed
• [x] All tests have passed
• [x] I have updated the documentation accordingly, if needed.

Additional Information

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (3593a29) 96.32% compared to head (5d685d4) 96.33%.

:exclamation: Current head 5d685d4 differs from pull request most recent head 3544243. Consider uploading reports for the commit 3544243 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #239 +/- ## ======================================= Coverage 96.32% 96.33% ======================================= Files 34 34 Lines 1550 1554 +4 ======================================= + Hits 1493 1497 +4 Misses 57 57 ``` | [Impacted Files](https://app.codecov.io/gh/jama5262/jiffy/pull/239?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jama+Mohamed) | Coverage Δ | | |---|---|---| | [lib/src/jiffy.dart](https://app.codecov.io/gh/jama5262/jiffy/pull/239?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jama+Mohamed#diff-bGliL3NyYy9qaWZmeS5kYXJ0) | `98.83% <100.00%> (+0.01%)` | :arrow_up: | | [lib/src/locale/supported\_locales.dart](https://app.codecov.io/gh/jama5262/jiffy/pull/239?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jama+Mohamed#diff-bGliL3NyYy9sb2NhbGUvc3VwcG9ydGVkX2xvY2FsZXMuZGFydA==) | `100.00% <100.00%> (ø)` | |

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