Treat `:Gvdiffsplit!` as a single file

[sand4rt]

When resolving merge conflicts using :Gvdiffsplit!, fugitive opens vertical diff splits for the conflicting versions, which is super usefull. However, after resolving the conflicts and moving on to a new file (one that has no conflicts), the diff splits remain open.

It would be great if :Gvdiffsplit! (or some related mechanism) could automatically close these extra diff splits once the user opens a new file. I can't think of a case where someone would want to keep those diffs open after switching files.

Proposed Behavior:

• Automatically close the extra diff splits (e.g., LOCAL, REMOTE) when opening a new file
• Would also be nice if :Gvdiffsplit! could run automaticly once a file with a merge conflict is opned, but that's probably out of scope so i asked it here: https://github.com/tpope/vim-fugitive/discussions/2416