Fix no targets for invocation for abstract this type

[CaelmBleidd]

Description

Add support for testing methods of the abstract classes which have instantiable inheritors. Early we didn't check whether we can create a this instance or not, now we can replace it with its inheritors if there is such an inheritors with non-overridden method under test.

Fixes #1624

Type of Change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

Regression and integration tests

The same as automatic tests/

Automated Testing

org.utbot.examples.objects.AbstractAnonymousClassTest#testNonOverriddenMethod

Manual Scenario

Run the contest estimator for org.antlr.v4.codegen.Target.getTemplates and check that there are no errors.

Checklist:

• The change followed the style guidelines of the UTBot project
• Self-review of the code is passed
• The change contains enough commentaries, particularly in hard-to-understand areas
• New documentation is provided or existed one is altered
• No new warnings
• New tests have been added
• All tests pass locally with my changes