Replace `graphemer` to `unicode-segmenter/grapheme` in the Bluesky app

[cometkim]

Note: Bluesky is an RN app, so they cannot rely on the platform-provided Intl.Segmenter

Manifest & Docs:

• https://github.com/es-tooling/module-replacements/blob/main/docs/modules/grapheme.md

Opened PRs:

• https://github.com/bluesky-social/atproto/pull/2563
• https://github.com/bluesky-social/social-app/pull/4452