feat: #1455 improve input decoration enabled property

[deandreamatias]

Connection with issue(s)

Close #1455

Connected to flutter/flutter#161602

Solution description

• Add an assert to warning the developer to avoid decoration.enabled use

Screenshots or Videos

To Do

• Read contributing guide
• Check the original issue to confirm it is fully satisfied
• Add solution description to help guide reviewers
• Add unit test to verify new or fixed behaviour
• If apply, add documentation to code properties and package readme

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 90.25%. Comparing base (ec7543b) to head (284faa1).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/src/form_builder_field_decoration.dart	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1464      +/-   ##
==========================================
+ Coverage   90.08%   90.25%   +0.16%     
==========================================
  Files          21       21              
  Lines         827      831       +4     
==========================================
+ Hits          745      750       +5     
+ Misses         82       81       -1     

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