Transparency: isolation mode and opacity mask editing can't be entered from each other

Enter Isolation Mode worked while an opacity mask was edited, and Edit
Opacity Mask and View Opacity Mask worked in isolation mode, so each
mode replaced the other's isolated art. In the reference app, isolation
mode can't be entered while a mask is edited, and mask editing can't be
entered in isolation mode.

object.isolate and perspective.editText, which shows type in isolation
mode, are now off while an opacity mask is edited, and a call returns
an error that ends "stop editing the opacity mask first". In isolation
mode transparency.editOpacityMask and transparency.viewOpacityMask are
off, and transparency.makeOpacityMask refuses one target, an object or
a layer, which it would take into mask editing; a call returns an error
that ends "exit isolation mode first". Make Opacity Mask with two
objects still masks one with the other. Pattern editing mode does not
count as isolation mode for these commands.

Object > Perspective > Edit Text, the canvas context menu and the
Transparency panel's menu and Make Mask button follow the commands'
enablement. A click or Alt-click on the mask thumbnail in isolation
mode shows the error and does not edit the mask. While a mask is
edited, the Contextual Task Bar leaves out Isolate, and the Properties
panel's Quick Actions leave out Isolate Group.

Docs: docs/mcp.md, docs/target-app-parity.md.

crates/engine/src/cmd/object/commands.rs

@@ -240,8 +240,8 @@ pub fn specs() -> Vec<CommandSpec> {
             "Enter Isolation Mode",
             [],
             None,
-            "{id?} isolate a group, a layer or a single object (default: the first selected object); type, a hidden or locked object, an object in a hidden or locked group or layer, and a guide path while Lock Guides is on are refused",
-            has_doc,
+            "{id?} isolate a group, a layer or a single object (default: the first selected object); type, a hidden or locked object, an object in a hidden or locked group or layer, and a guide path while Lock Guides is on are refused, and so is every object while an opacity mask is edited",
+            crate::cmd::maskedit::outside_mask_editing,
             isolate
         ),
         cmd!("object.exitIsolation", "Exit Isolation Mode", [], None, "{}", has_doc, exit_isolation),