Description

Currently if we call action on interface or abstract class - the action to Generate tests with UnitTestBot... is not available.
But there can be nested classes and static methods inside.
Suggest test generation for them.

To Reproduce

1. Run the 'lrs' project in IntelliJ Idea with installed UnitTestBot plugin
2. Find abstract class LongRangeSet in Project view tree
3. Call Generate tests with UnitTestBot... action either from context menu or from inside the class

Expected behavior

UnitTestBot dialog with nested classes as members should be opened.
There are 5 nested final classes inside and several static methods: LongRangeSet.divide() fore example.

Actual behavior

UnitTestBot dialog is not opened.
Notification is shown: Generate tests with UtBot for the abstract class or interface LongRangeSet is not supported.

Visual proofs (screenshots, logs, images)

Environment

IntelliJ IDEA - all supported versions