Fixes for EF Core owned entities

[bkoelman]

This PR fixes two problems when using owned entities:

1. Owned entity properties are not retrieved when using sparse fieldsets (because they are modeled as navigations in EF Core, instead of scalar properties).
2. When producing a LINQ query that includes an owned entity, EF Core produces an error, indicating that the query must be marked as non-tracked. Due to potential performance impact, a virtual method is provided that enables tweaking the behavior.

Closes #1271.

QUALITY CHECKLIST

• Changes implemented in code
• Complies with our contributing guidelines
• Adapted tests
• N/A: Documentation updated

[codecov]

Codecov Report

Merging #1272 (ff4802c) into master (627bae9) will decrease coverage by 0.17%.
The diff coverage is 88.23%.

❗ Current head ff4802c differs from pull request most recent head 779daea. Consider uploading reports for the commit 779daea to get more accurate results

@@            Coverage Diff             @@
##           master    #1272      +/-   ##
==========================================
- Coverage   92.98%   92.82%   -0.17%     
==========================================
  Files         255      255              
  Lines        8242     8233       -9     
==========================================
- Hits         7664     7642      -22     
- Misses        578      591      +13     

Impacted Files	Coverage Δ
...Core/Repositories/EntityFrameworkCoreRepository.cs	96.03% <77.77%> (-0.59%)	⬇️
.../Internal/QueryableBuilding/SelectClauseBuilder.cs	99.14% <100.00%> (+0.01%)	⬆️
...DotNetCore/Resources/ResourceDefinitionAccessor.cs	100.00% <100.00%> (ø)

... and 6 files with indirect coverage changes