Add generics support

[maybetm]

Hi! ☺️ I noticed that the MapStruct IDEA plugin didn't support generics properly in some cases.
This PR adds support for generic types. I'd appreciate it if you could review and merge these changes!

Before

After

[hduelme]

@maybetm, good catch! I left a few comments for you. Could you also add tests covering the other branches?

[hduelme]

Why did you changes this code? I think this could break building on other OS (Windows)

[maybetm]

I added this specifically to ensure the tests run correctly on Windows. Without these configurations, the testing framework is unable to access packages

[maybetm]

For example, before fix

14:52:40,037 FINE   .intellij.openapi.command.impl - finishCommand: name = Renaming method setTestName(String) of class org.mapstruct.intellij.test.examples.SimpleMapper.Target to setNewName, groupId = null 
14:52:40,039 SEVERE                 #TestFramework - Test failed 
com.intellij.openapi.vfs.newvfs.impl.VfsRootAccess$VfsRootAccessNotAllowedError: File accessed outside allowed roots: file://D:/projects/github/mapstruct-idea/testData/usages/RenameTargetReferenceAfter.java; 

[hduelme]

@maybetm did you have the project not on your main disc (C:)?

[hduelme]

@maybetm sorry for the late response. I saw that you fixed my previous findings.
The only thing still open is the change insrc/test/java/org/mapstruct/intellij/MapstructBaseCompletionTestCase.java. I’m still not sure whether this change is needed. Could you provide some more information about your environment and why the change is required?

I’ll re-review your PR soon.