editor: move docs toggle from settings

This removes the docs toggle switch from the settings and adds a new
docs toggle button to the editor.

Fixes: https://github.com/pybricks/support/issues/778

src/editor/editor.scss

@@ -93,4 +93,11 @@
             color: bp.$pt-dark-text-color-muted;
         }
     }
+
+    &-doc-button {
+        position: absolute;
+        bottom: bp.$pt-grid-size;
+        right: bp.$pt-grid-size;
+        z-index: bp.$pt-z-index-overlay;
+    }
 }