test: split and improve ObjectFieldMapTypeHandlerFactoryTests

[jdrueckert]

• split into multiple tests to avoid testing different aspects in single test
• remove usage of implicit member type knowledge in assertion phase
• add negative assertions to ensure only expected calls are made
• improve test case documentation

Once #5154 is merged, we'll need to update the suppression of UUF_UNUSED_FIELD spotbugs findings for SingleTypeClass and MultiTypeClass.

[jdrueckert]

Failing test ExampleTest.testClientConnection is a known sporadic and unrelated to code changes in this PR. Merging despite the failing test.