Similar to microsoft/vscode-pull-request-github#1622, have the same behavior for the queries in the PR tree

Especially in the light of #151 , it would be great if people could just re-generate the whole Id file.

On the following example:

@
-fn func(a,b,c) {
-  x = g(a,b)
-  y = if x {
-          h(b,c)
-      } else {
-          0
-      }
-  return x + y
-}
+// fn func(a,b,c) {
+//   x = g(a,b)
+//   y = if x {
+//           h(b,c)
+//       } else {
+//           0
+//       }
+//   return x + y
+// }

diffr displays the diff like that:
![image](https://user-images.g

It would be nice if diff-goto-source (C-c C-c) worked when this is invoked from github-review-forge-pr-at-point. All it needs to do is set the current directory to the git working tree in the diff-mode buffer. In many cases it does not matter too much whether the user has the "correct" branch is checked out - it just needs to be close.