Remove unused stuff
[diff] IDEA-77540 Go To Source from vcs diff

Go To Source uses the getOpenFileDescriptor() returned by DiffContent,
but it is null for BinaryContent & SimpleContent,
both used from different places of the VCS history.

* Implement it for BinaryContent:
  - get the file by path if exists
  - supply the Project to the constructor, deprecate other constructors.

* SimpleContent is too general thing and is used everywhere,
  so for certain VCS operations create a separate extension -
  OpenFileCapableSimpleContent which behaves the same way: searches
  the virtual file by path.

KNOWN LIMITATION:
current implementation navigates to the same offset,
no conversion is made if the file is different from the current
version.
IDEA-91148 Difficult to step over code due to tooltips
[git] IDEA-119322 Use "unsorted" only since Git 1.7.12.1