feat: support text align in text-based blocks

[LucasXu0]

added support for customizing the text alignment for each block.

  /// The text align of a block component.
  ///
  /// This value is only available for the block with text,
  /// e.g. paragraph, heading, quote, to-do list, bulleted list, numbered list
  final TextAlign Function(Node node) textAlign;

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.16%. Comparing base (6c54748) to head (03afbb3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1002   +/-   ##
=======================================
  Coverage   72.16%   72.16%           
=======================================
  Files         319      319           
  Lines       15243    15246    +3     
=======================================
+ Hits        11000    11003    +3     
  Misses       4243     4243           

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