Add alignment configuration to FDialogContentStyle

[elrizwiraswara]

Describe the changes

First off, thank you for Forui. I've been using it for several months now and the
experience has been great.

While moving to the latest version, I noticed the dialog styling changed. Most of it can
be adjusted through FThemeData.dialogStyle, but the content's cross-axis (vertical)
alignment cannot. The earlier changelog notes this change:

Breaking Change VerticalContent alignment from center to start.

I personally prefer the previous centered content alignment. Right now the only way to get
it back is a custom FDialog.raw, which is awkward to apply consistently across an entire
app. Being able to set it once on FThemeData.dialogStyle would be much simpler, so this PR
adds that:

• Add FDialogContentStyle.crossAxisAlignment to control how the image, title, body, and
  actions align along the cross axis.
• Add FDialogContentStyle.titleTextAlign and FDialogContentStyle.bodyTextAlign to control
  the title/body text alignment.
• All three default to start, so existing behavior is unchanged (non-breaking).
• Content now reads these from the style instead of hardcoding them. Because the fields are
  keyed by the dialog's axis variant, horizontal and vertical layouts can be aligned
  independently.

Checklist

• I have read the CONTRIBUTING.md.
• I have included the relevant unit/golden tests.
• I have included the relevant samples.
• I have updated the documentation accordingly.
• I have added the required flutters_hook for widget controllers.
• I have updated the CHANGELOG.md if necessary.

[Pante]

Thanks for filing a PR, unfortunately I'm putting this PR on hold as we evaluate shifting certain widget's content/layouts to being purely CLI generated instead.