feat: add default keybindings for changing the mask brush size

Make it easier to change the mask brush size. These keybindings are
familiar to users of other image editors.

Author: davvid-comfy

src/constants/coreKeybindings.ts

@@ -82,6 +82,18 @@ export const CORE_KEYBINDINGS: Keybinding[] = [
     },
     commandId: 'Comfy.ShowSettingsDialog'
   },
+  {
+    combo: {
+      key: '['
+    },
+    commandId: 'Comfy.MaskEditor.BrushSize.Decrease'
+  },
+  {
+    combo: {
+      key: ']'
+    },
+    commandId: 'Comfy.MaskEditor.BrushSize.Increase'
+  },
   // For '=' both holding shift and not holding shift
   {
     combo: {