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/workspace/src/workspace_settings.rs

@@ -8,6 +8,8 @@ use settings::{Settings, SettingsSources};
 #[derive(Deserialize)]
 pub struct WorkspaceSettings {
     pub active_pane_magnification: f32,
+    pub pane_split_direction_horizontal: PaneSplitDirectionHorizontal,
+    pub pane_split_direction_vertical: PaneSplitDirectionVertical,
     pub centered_layout: CenteredLayoutSettings,
     pub confirm_quit: bool,
     pub show_call_status_icon: bool,
@@ -61,6 +63,14 @@ pub struct WorkspaceSettingsContent {
     ///
     /// Default: `1.0`
     pub active_pane_magnification: Option<f32>,
+    // Direction to split horizontally.
+    //
+    // Default: "up"
+    pub pane_split_direction_horizontal: Option<PaneSplitDirectionHorizontal>,
+    // Direction to split vertically.
+    //
+    // Default: "left"
+    pub pane_split_direction_vertical: Option<PaneSplitDirectionVertical>,
     // Centered layout related settings.
     pub centered_layout: Option<CenteredLayoutSettings>,
     /// Whether or not to prompt the user to confirm before closing the application.
@@ -131,6 +141,20 @@ pub enum AutosaveSetting {
     OnWindowChange,
 }
 
+#[derive(Copy, Clone, Debug, Serialize, Deserialize, PartialEq, Eq, JsonSchema)]
+#[serde(rename_all = "snake_case")]
+pub enum PaneSplitDirectionHorizontal {
+    Up,
+    Down,
+}
+
+#[derive(Copy, Clone, Debug, Serialize, Deserialize, PartialEq, Eq, JsonSchema)]
+#[serde(rename_all = "snake_case")]
+pub enum PaneSplitDirectionVertical {
+    Left,
+    Right,
+}
+
 #[derive(Copy, Clone, Debug, Serialize, Deserialize, JsonSchema)]
 #[serde(rename_all = "snake_case")]
 pub struct CenteredLayoutSettings {