Improve autovalidate modes

[deandreamatias]

Connection with issue(s)

Close #1157

Connected to flutter/flutter#125766

Solution description

Improve how use autovalidateMode property on internal Form and Field Form states.
I thinks that's solution isn't perfect because exist a bug on Flutter Framework that create conflict in some cases when use different autovalidateMode on Form and on Field Form. I reported about this issue here

Screenshots or Videos

Screencast.from.30-04-23.19.30.00.webm

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

Merging #1232 (0e0f0e8) into main (f5a831b) will increase coverage by 0.94%.
The diff coverage is 88.23%.

@@            Coverage Diff             @@
##             main    #1232      +/-   ##
==========================================
+ Coverage   85.21%   86.15%   +0.94%     
==========================================
  Files          19       20       +1     
  Lines         710      715       +5     
==========================================
+ Hits          605      616      +11     
+ Misses        105       99       -6     

Impacted Files	Coverage Δ
lib/src/form_builder.dart	76.54% <75.00%> (+3.70%)	⬆️
lib/src/form_builder_field.dart	82.65% <90.00%> (+3.48%)	⬆️
lib/src/extensions/autovalidatemode_extension.dart	100.00% <100.00%> (ø)

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