Add option to set split direction (#16345)

This adds an option to set the split direction for both the horizontal
splits, and the vertical splits.

A couple of things to look for when reviewing:

* The `derive` keywords on the Enums were copy pasted, no clue what they
should be
* Tried adding tests for this, but got stuck.

Co-authored with @Tobbe

Fixes: https://github.com/zed-industries/zed/issues/11342

crates/vim/src/command.rs

@@ -529,8 +529,8 @@ fn generate_commands(_: &AppContext) -> Vec<VimCommand> {
             save_intent: Some(SaveIntent::Overwrite),
         }),
         VimCommand::new(("cq", "uit"), zed_actions::Quit),
-        VimCommand::new(("sp", "lit"), workspace::SplitUp),
-        VimCommand::new(("vs", "plit"), workspace::SplitLeft),
+        VimCommand::new(("sp", "lit"), workspace::SplitHorizontal),
+        VimCommand::new(("vs", "plit"), workspace::SplitVertical),
         VimCommand::new(
             ("bd", "elete"),
             workspace::CloseActiveItem {