Enable nullability in TabPageCollectionEditor

[gpetrou]

Proposed changes

• Enable nullability in TabPageCollectionEditor.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Attention: Patch coverage is 37.50000% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 74.32392%. Comparing base (b95d01b) to head (fab2943).

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #11283         +/-   ##
===================================================
+ Coverage   74.32164%   74.32392%   +0.00227%     
===================================================
  Files           3028        3028                 
  Lines         627287      627296          +9     
  Branches       46765       46767          +2     
===================================================
+ Hits          466210      466231         +21     
+ Misses        157729      157719         -10     
+ Partials        3348        3346          -2     

Flag	Coverage Δ
Debug	74.32392% <37.50000%> (+0.00227%)	⬆️
integration	17.99491% <0.00000%> (-0.00162%)	⬇️
production	47.08476% <37.50000%> (+0.00589%)	⬆️
test	96.98888% <ø> (ø)
unit	44.06018% <37.50000%> (+0.00458%)	⬆️

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[Epica3055]

looks good 😁

[LeafShi1]

Using is {} obj can more simpler

      if (TypeDescriptor.CreateInstance(host, itemType, argTypes: null, args: null) is { } obj)
      {
          return obj;
      }

      throw new InvalidOperationException(
          string.Format(
          SR.CollectionEditorCreateInstanceError,
          nameof(IDesignerHost),
          nameof(TypeDescriptor),
          itemType.FullName));