Throw on unsupported includes

[phnx47]

An includes expression now has to name a property marked with a join attribute, and anything else raises an ArgumentException naming the property rather than being silently dropped from the query. Update with joins is also rejected for every provider except MySQL, since UPDATE t1 JOIN t2 ON ... SET ... is MySQL syntax that SQL Server, PostgreSQL, Oracle and SQLite all refuse to parse. Passing a join whose navigation property is null still works and simply skips that join, so nothing that generates valid SQL today starts throwing.

Ref #581

[codecov]

Codecov Report

❌ Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.33%. Comparing base (911cc9f) to head (73e2427).

Files with missing lines	Patch %	Lines
src/SqlGenerator/SqlGenerator.GetUpdate.cs	71.42%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #583      +/-   ##
==========================================
+ Coverage   64.05%   64.33%   +0.27%     
==========================================
  Files          59       59              
  Lines        1992     1999       +7     
  Branches      395      396       +1     
==========================================
+ Hits         1276     1286      +10     
+ Misses        573      572       -1     
+ Partials      143      141       -2     

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