[vcs] Don't wrap FilePath creation into read action

There is no point in this read action, but it takes the lock => may
slow down if the utility method is used during a large VCS process
(even if taken atomically).

VCS requires file content rarely, so the only benefit from this read
was in the situation, if a VirtualFile gets created when we've
already went to createForDeletedFile (and similar situations).
However, it is not a big deal, especially since VirtualFile is
refreshed inside the FilePathImpl.
[vcs] Remove read action from loading byte content from java.io.File
Don't mark PairFunction return type as Nullable

Otherwise it requires all clients to check for null.
[log] IDEA-119316 Fix "go to commit" if there are log filters

jumpToCommit used to consider only the graphical DataPack.

* Delegate to the concrete AbstractVcsLogTableModel to find row by hash.
* If not found, request more if possible and search again.
* If not found, and all data has been loaded, show a message.