Remove Panel accessible role from the root node, and unknown nodes (fixes issues on Windows)

This fixes issues on Windows:

1. Windows pronounced "Panel unavailable" at start
2. When we focus on Switch or Box(Modifier.clickable), there was "Panel0" pronounced. Now it says nothing.
3. After merging #881 refocus the main component. This leads to pronouncing the window title, now it says nothing, as the accessible root node is unknown

on macOs it doesn't change anything

## Testing
Manually with accessibility enabled on run1 (Windows, macOs)

Author: igordmn

compose/ui/ui/src/desktopMain/kotlin/androidx/compose/ui/platform/ComposeAccessible.kt

@@ -402,7 +402,7 @@ internal class ComposeAccessible(
                 setText != null -> AccessibleRole.TEXT
                 text != null -> AccessibleRole.LABEL
                 progressBarRangeInfo != null -> AccessibleRole.PROGRESS_BAR
-                else -> AccessibleRole.PANEL
+                else -> AccessibleRole.UNKNOWN
             }
         }
 

compose/ui/ui/src/desktopMain/kotlin/androidx/compose/ui/platform/ComposeSceneAccessible.kt

@@ -153,7 +153,7 @@ internal class ComposeSceneAccessible(
         }
 
         override fun getAccessibleRole(): AccessibleRole {
-            return AccessibleRole.PANEL
+            return AccessibleRole.UNKNOWN
         }
 
         override fun getAccessibleStateSet(): AccessibleStateSet {