Completely change json error response

[jwag956]

Now return errors is always a simple list of errors.
we also return field_errors - which is the old wtforms dict of errors.

Support new wtforms 3.0 form level errors.

[codecov]

Codecov Report

Merging #638 (1cbd618) into master (0bf4f8e) will decrease coverage by 0.01%.
The diff coverage is 96.42%.

@@            Coverage Diff             @@
##           master     #638      +/-   ##
==========================================
- Coverage   98.06%   98.04%   -0.02%     
==========================================
  Files          31       31              
  Lines        4338     4347       +9     
==========================================
+ Hits         4254     4262       +8     
- Misses         84       85       +1     

Impacted Files	Coverage Δ
flask_security/utils.py	97.36% <93.75%> (-0.19%)	⬇️
flask_security/tf_plugin.py	99.22% <100.00%> (+<0.01%)	⬆️
flask_security/unified_signin.py	98.77% <100.00%> (ø)
flask_security/views.py	98.73% <100.00%> (+<0.01%)	⬆️
flask_security/webauthn.py	98.65% <100.00%> (ø)

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