[csharp][generichost] Implement not required nullable properties #16810

JUnit Test results ✅

Report	Passed	Time
modules/openapi-generator-cli/target/surefire-reports/TEST-TestSuite.xml	48✅	6s
modules/openapi-generator-core/target/surefire-reports/TEST-TestSuite.xml	15✅	1s
modules/openapi-generator-maven-plugin/target/surefire-reports/TEST-org.openapitools.codegen.plugin.CodeGenMojoTest.xml	4✅	7s
modules/openapi-generator/target/surefire-reports/TEST-TestSuite.xml	1997✅	75s

48 tests were completed in 6s with 48 passed, 0 failed and 0 skipped.

Test suite	Passed	Failed	Skipped	Time
TestSuite	48✅			6s

15 tests were completed in 1s with 15 passed, 0 failed and 0 skipped.

Test suite	Passed	Failed	Skipped	Time
TestSuite	15✅			1s

4 tests were completed in 7s with 4 passed, 0 failed and 0 skipped.

Test suite	Passed	Failed	Skipped	Time
org.openapitools.codegen.plugin.CodeGenMojoTest	4✅			7s

1997 tests were completed in 75s with 1997 passed, 0 failed and 0 skipped.

Test suite	Passed	Failed	Skipped	Time
TestSuite	1997✅			75s