[Git] IDEA-59587 again. Moved New files are marked as not changed.

[Git] IDEA-59587 again. Moved New files are marked as not changed.

Root cause: comparing VirtualFiles when identifying who is the ancestor, while VirtualFile has changed due to the file move.
1. Don't work with FilePaths - instead compare paths as Strings sorted lexicographically. This might leave extra paths, but it's faster.
2. Add a test for the bug.

[Reviewed by Max]
(cherry picked from commit de3ff0576939ffc4412e0228dd6103825cdd2a73)

Conflicts:

	plugins/git4idea/tests/git4idea/tests/GitChangeProviderTest.java