feat(split): add right to left support

See https://github.com/nathancahill/split/issues/739

packages/splitjs/index.d.ts

@@ -44,6 +44,9 @@ declare namespace Split {
         // Direction to split: horizontal or vertical.
         direction?: 'horizontal' | 'vertical'
 
+        // If the UI is right-to-left. Affects the drag direction.
+        rtl?: boolean
+
         // Cursor to display while dragging.
         cursor?: string
 

packages/splitjs/src/split.js

@@ -182,6 +182,7 @@ const Split = (idsOption, options = {}) => {
         defaultElementStyleFn,
     )
     const gutterStyle = getOption(options, 'gutterStyle', defaultGutterStyleFn)
+    const rtl = getOption(options, 'rtl', false)
 
     // 2. Initialize a bunch of strings based on the direction we're splitting.
     // A lot of the behavior in the rest of the library is paramatized down to
@@ -621,6 +622,7 @@ const Split = (idsOption, options = {}) => {
 
             // if the parent has a reverse flex-direction, switch the pair elements.
             if (
+                (direction === HORIZONTAL && rtl) ||
                 parentFlexDirection === 'row-reverse' ||
                 parentFlexDirection === 'column-reverse'
             ) {