docs: standardize on "layout generator"

This is likely more clear than "layout client" to most users.

river/Cursor.zig

@@ -674,7 +674,7 @@ pub fn enterMode(self: *Self, mode: std.meta.Tag((Mode)), view: *View) void {
             }
 
             // Automatically float all views being moved by the pointer, if
-            // their dimensions are set by a layout client. If however the views
+            // their dimensions are set by a layout generator. If however the views
             // are unarranged, leave them as non-floating so the next active
             // layout can affect them.
             if (!view.current.float and view.output.current.layout != null) {