replay: Simplify FileEditor implementation

Instead of maintaining file state based on svn properties across revisions
replay and trying to reconstruct the same file as with a svn export operation
after applying text deltas, prefer to simply export the file from the currently
processed revision when closing the associated file editor.

This greatly simplify the replay module implementation while approximatively
keeping the same performance as before.

Also add a test that would fail without these changes.

Related to T4673