Isolation mode: double-clicking a single object isolates it

With Double Click To Isolate on, the Selection tool isolated groups only. A
double-click on a single path, compound path, image, mesh or placed file now
isolates it too, as the public documentation describes. Type still switches to
the Type tool; blends, envelopes, repeats and symbol instances keep their own
editing modes.

While a single object is isolated only it is hit, marqueed and taken by Select
All, new art goes beside it in its group or layer, and a double-click on the
empty canvas leaves with it selected. object.isolate accepts any object except
type.

docs/mcp.md

@@ -1159,7 +1159,7 @@ and `layerRows`, the rows highlighted in the panel.
   `layer.reverse {ids?}`, `layer.template {ids?, on?}`, `layer.hideOthers` / `layer.showAll`,
   `layer.outlineOthers` / `layer.previewAll`, `layer.lockOthers` / `layer.unlockAll` (Alt-clicking an eye or a lock
   runs Hide or Lock Others for the row's layer, or Show or Unlock All when the others already are), `layer.pasteRemembersLayers`,
-  `object.isolate {id}` / `object.exitIsolation`.
+  `object.isolate {id}` (a group, a layer or a single object; not type) / `object.exitIsolation`.
 - **Dialogs and panel state** (control channel and the app's MCP): `ui.layerOptions {ids?}` and `ui.newLayer
   {sublayer?}` open Layer Options (dialog `layerOptions`: name, color, template, locked, visible, printable, preview,
   dimImages, dimPercent; OK is one undo step), `ui.layersPanelOptions` opens Panel Options (`layersPanelOptions`:
@@ -1572,7 +1572,8 @@ The Selection & Anchor Display and General preferences apply to `pointer_gesture
 - `ctrlClickSelectsBehind` (on by default): a Selection tool click with `mods: {cmd: true}` (Command on macOS, Ctrl
   elsewhere) selects the object under the selected one there, the next such click the one under that, then the
   topmost again. Cmd held to borrow the selection tool from another tool clicks as usual.
-- `doubleClickToIsolate` (on by default): off, a `doubleclick` on a group with the Selection tool no longer isolates it.
+- `doubleClickToIsolate` (on by default): a `doubleclick` with the Selection tool isolates a group, a compound path or a
+  single path, image, mesh or placed file (not type, blends, envelopes, repeats or symbol instances); off, it no longer does.
 - `usePreciseCursors`: the Pen, Eyedropper, Slice and Blend tools' pointers are a crosshair.
 - `snapToPointTolerance` (1–8 px, 2 by default): with View › Snap to Point on and Smart Guides off (desktop app), the
   point a selection is dragged by, a drawn point and a transform tool's reference point land on an anchor or a ruler