Bug 447554 - gcov not handling linked files

- Fix number of runs counter to come from program summary
  instead of object summary as that has been obsoleted
- Fix logic to handle case where we end up with an IFileEditorInput
  and we want an IFileStore (don't return null and end up
  using a source-not-found editor)
- Add a method to get all projects we are tracking for gcov
- Add a visitor class to search a project for a linked-in
  resource we are trying to open from the gcov view

Change-Id: Ieeb4c8a047a95da239e7b625f717a1d44fad8f31
Reviewed-on: https://git.eclipse.org/r/35155
Reviewed-by: Roland Grunberg <rgrunber@redhat.com>
Tested-by: Roland Grunberg <rgrunber@redhat.com>