Preserve the revealed area after using "Open File" from git-diff editor (fix #53465)

[Hirico]

Ref: #53465.

[Hirico]

Effect gif:

As you can see, both cursor position and view position are preserved now.

Limitations:

1. I didn't change what would happen when you first open the diff editor (so in that scenario, previous view position is still ignored). Intuitively, when you invoke command "Git: Open Changes", the view position should be preserved, too. I didn't do it because I'm not quite sure of requirements on that.

2. I use editor.visibleRanges to get previous view position, and there is an issue on that. If you put the cursor on the left column, and then click "Open File", the view position (of the opened right file) will follow the line numbers of the left column, leading you to a strange position. I guess we can change visibleRanges implementation of DiffEditor for this?

[joaomoreno]

Thanks! 🍻