Previously we would render the diff for a directory to the main/secondary pair,
but a diff for a file to the staging/stagingSecondary pair. (And similar for
commit files: main/secondary for directories, but
patchBuilding/patchBuildingSecondary for files.)
I always found this confusing and couldn't really understand why we are doing
this; but now it gets in my way because I want to attach a controller to
main/secondary so that they can be focused. So change it to always use the main
context pair for everything we render from a side panel.
Assert the entire lines using Equals instead of Contains. This makes the tests a
bit easier to read, and it makes it much easier to decide how they need to be
changed when we change the layout (like we do in the last commit of this
branch).
It is true that this requires changing all these tests for any future UI
changes, but I think this is a good price to pay; those adaptions are trivial
and can be done without thinking.
