[BUG][Csharp][GenericHost] Client serialization of oneOf repeats discriminator

[gerwinjansen]

Fixes #16597 @mandrean @shibayan @Blackclaws @lucamazzanti @iBicha

In case of a submodel with sub-submodel (e.g. Shape with submodel Triangle, which has submodel EquilateralTriangle), the removal of the properties must start from the root. If Triangle is cleaned first, then Shape doesn't know which properties to remove anymore.

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[devhl-labs]

This is an obvious improvement, though what I would really like to see is for the discriminator string not be in any of the classes. Once you're in the class, the discriminator is known, so requiring a string in the constructor is redundant. See this Whale constructor. We known it's a whale, so the string doesn't really need to be there at all. It's okay if we want to merge this though since it appears to fix the problem.

[wing328]

@gerwinjansen can you please take a look at the test failure when you've time?

https://github.com/OpenAPITools/openapi-generator/actions/runs/7247593357/job/20330032075?pr=17397

[gerwinjansen]

@wing328: I fixed it, it is ready for the next run. Please approve.

[wing328]

Error:  Failures: 
Error:    CSharpGenericHostDiscriminatorTest.oneOfWithReferencesAndDiscriminatorTest:43 » NullPointer
Error:  Tests run: 2110, Failures: 1, Errors: 0, Skipped: 0
Error:  Failed to execute goal org.apache.maven.plugins:maven-surefire-plugin:3.0.0:test (default-test) on project openapi-generator: There are test failures.
Error:  
Error:  Please refer to /home/runner/work/openapi-generator/openapi-generator/modules/openapi-generator/target/surefire-reports for the individual test results.
Error:  Please refer to dump files (if any exist) [date].dump, [date]-jvmRun[N].dump and [date].dumpstream.
Error:  -> [Help 1]
Error:  
Error:  To see the full stack trace of the errors, re-run Maven with the -e switch.
Error:  Re-run Maven using the -X switch to enable full debug logging.
Error:  
Error:  For more information about the errors and possible solutions, please read the following articles:

can you please take a look at the build failure when you've time?

ref: https://github.com/OpenAPITools/openapi-generator/actions/runs/8052044583/job/22465390581?pr=17397

[gerwinjansen]

@wing328: I fixed it, it is ready for the next run. Please approve.

[devhl-labs]

This change wont be needed once my remove discrim pr is merged.

[devhl-labs]

Can you try my branch to see if it works for you? https://github.com/OpenAPITools/openapi-generator/pull/18445

[gerwinjansen]

@devhl-labs: yes, it works for me. This PR can be closed without merge if your PR gets approved.