Fix broken coordinate input in Entity table

[soininen]

The latitude, longitude and altitude fields now accept non-localized numbers properly and handle Nones gracefully.

Fixes #3207

Checklist before merging

• Documentation is up-to-date
• Release notes have been updated
• Unit tests have been added/updated accordingly
• Code has been formatted by black & isort
• Unit tests pass

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.00%. Comparing base (20f7984) to head (fb4811b).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
...oolbox/spine_db_editor/widgets/custom_delegates.py	36.36%	7 Missing ⚠️
...oolbox/spine_db_editor/widgets/graph_view_mixin.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3208      +/-   ##
==========================================
- Coverage   69.00%   69.00%   -0.01%     
==========================================
  Files         198      198              
  Lines       38583    38588       +5     
  Branches     4631     4631              
==========================================
+ Hits        26626    26628       +2     
- Misses      10647    10650       +3     
  Partials     1310     1310              

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