Add integration tests for discarding dir changes when filtering by path

When discarding a directory, we only want to discard those files that are
visible in the current filter view. The tests show that this already works
correctly for discarding all changes, but it doesn't for discarding only
unstaged changes: in this case, untracked files are handled correctly, but
changes to tracked files are discarded without respecting the filter.

pkg/integration/tests/test_list.go

@@ -215,9 +215,11 @@ var tests = []*components.IntegrationTest{
 	file.CopyMenu,
 	file.DirWithUntrackedFile,
 	file.DiscardAllDirChanges,
+	file.DiscardAllDirChangesWhenFiltering,
 	file.DiscardRangeSelect,
 	file.DiscardStagedChanges,
 	file.DiscardUnstagedDirChanges,
+	file.DiscardUnstagedDirChangesWhenFiltering,
 	file.DiscardUnstagedFileChanges,
 	file.DiscardUnstagedRangeSelect,
 	file.DiscardVariousChanges,