fix: update font_awesome_flutter to v11.0.0

[christianmemije]

What kind of change does this PR introduce?

Bug fix & compatibility update.

What is the current behavior?

In Flutter 3.24+, IconData was changed to a final class. This causes older versions of font_awesome_flutter (< 11.0.0) to fail compilation (exit code 254) because they attempt to extend IconData.
Currently, supabase_auth_ui restricts font_awesome_flutter to < 11.0.0 and hardcodes its icon implementation to expect standard IconData types, preventing users on modern Flutter from compiling successfully.

Fixes #151

What is the new behavior?

• Bumps font_awesome_flutter dependency to ^11.0.0 to resolve the IconData compile errors.
• Updates SupaSocialsAuth to use FaIconData and the FaIcon() widget for rendering social icons, as font_awesome_flutter 11+ no longer returns IconData for its brand icons.
• Replaces the fallback Icons.close with FontAwesomeIcons.xmark to not use the deprecated icon: 'close' is deprecated and shouldn't be used. Use "xmark" instead

Additional context

Tested on a Flutter 3.44+ where the previous implementation threw an exit code 254 compile error.

[RobK410]

can we please get this PR done so I dont have to override this project?

[bcorman]

@dshukertjr

This repo's been pretty quiet for a year so I'm not sure if you're still around, but if so would you be able to take a look?

[christianmemije]

@O8O7 @jadl456 Any guidance?