Enable nullability in some GridEntry members

[gpetrou]

Proposed changes

• Enable nullability in some GridEntry members.

Microsoft Reviewers: Open in CodeFlow

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 25.00000% with 42 lines in your changes are missing coverage. Please review.

Project coverage is 73.19443%. Comparing base (228f072) to head (c4718b5). Report is 6 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #10872         +/-   ##
===================================================
- Coverage   73.19977%   73.19443%   -0.00535%     
===================================================
  Files           3097        3097                 
  Lines         633890      633913         +23     
  Branches       47348       47357          +9     
===================================================
- Hits          464006      463989         -17     
- Misses        166332      166374         +42     
+ Partials        3552        3550          -2     

Flag	Coverage Δ
Debug	73.19443% <25.00000%> (-0.00535%)	:arrow_down:
integration	18.43047% <16.07143%> (-0.00010%)	:arrow_down:
production	46.67982% <25.00000%> (-0.00971%)	:arrow_down:
test	94.97091% <ø> (ø)
unit	43.58843% <21.42857%> (-0.00946%)	:arrow_down:

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