fix: Text Style on Flutter 3.22

[chandrabezzo]

Description

After Flutter SDK 3.22, removed deprecated text theme for headline6 and subtitle2. To fix this issue I follow migration guide from here.

Checklist

• [x] The title of my PR starts with a [Conventional Commit] prefix (fix:, feat:, docs: etc).
• [x] I have followed the [Contributor Guide] when preparing my PR.
• [ ] I have updated/added tests for ALL new/updated/fixed functionality.
• [ ] I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• [ ] I have updated/added relevant examples in examples or docs.

Breaking Change?

• [ ] Yes, this PR is a breaking change.
• [x] No, this PR is not a breaking change.

Related Issue

#434

Result

Follow Migration Guide

[VB10]

lgtm 🌸

here is an example of usage this pr:

 showcaseview: 
    git: 
      url: https://github.com/chandrabezzo/flutter_showcaseview
      ref: bugfix/text-theme/removed-3.22

[aditya-css]

Hello @chandrabezzo, Thank you for raising this PR. Can you please bump the version to 3.0.0 pubspec and changelog?

[chandrabezzo]

Done @aditya-css

[Obada2020]

how to pull this in my git

[victor337]

how to pull this in my git

I think he will update in pub.dev, but in the meantime use this:

showcaseview:
    git:
      url: https://github.com/chandrabezzo/flutter_showcaseview
      ref: ae8d8a327cdede529d264d1df02892fdc6161688