Respect layers order in accessibility (#1698)

Accessibility engine should respect layers order as well as should hide
the content under focusable layers.
Implement accessibility tests based on instrumented tests.

Fixes
https://youtrack.jetbrains.com/issue/CMP-7163/Focusable-layers-should-obscure-content-for-accessibility-reader

## Testing
Popups and dialogs should behave the same as they do on Android.

## Release Notes
### Fixes - iOS
- Accessibility reading of content when obscured by layers such as
pop-ups and dialogs.

compose/ui/ui/src/uikitInstrumentedTest/kotlin/androidx/compose/ui/accessibility/LayersAccessibilityTest.kt

@@ -0,0 +1,179 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package androidx.compose.ui.accessibility
+
+import androidx.compose.material.Text
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.ui.test.assertAccessibilityTree
+import androidx.compose.ui.test.runUIKitInstrumentedTest
+import androidx.compose.ui.window.Dialog
+import androidx.compose.ui.window.Popup
+import androidx.compose.ui.window.PopupProperties
+import kotlin.test.Test
+
+class LayersAccessibilityTest {
+
+    @Test
+    fun testNodesCoveredByPopup() = runUIKitInstrumentedTest {
+        val topPopup = mutableStateOf(false)
+        val bottomPopup = mutableStateOf(false)
+        val topPopupFocusable = mutableStateOf(false)
+        setContentWithAccessibilityEnabled {
+            Text("Root")
+            if (bottomPopup.value) {
+                Popup {
+                    Text("Popup 1")
+                }
+            }
+            if (topPopup.value) {
+                Popup(properties = PopupProperties(focusable = topPopupFocusable.value)) {
+                    Text("Popup 2")
+                }
+            }
+        }
+
+        assertAccessibilityTree {
+            label = "Root"
+        }
+
+        bottomPopup.value = true
+        // Non-focusable popup should not hide content under it for accessibility reader
+        assertAccessibilityTree {
+            node {
+                label = "Root"
+            }
+            node {
+                label = "Popup 1"
+            }
+        }
+
+        topPopup.value = true
+        // Non-focusable popup should not hide content under it for accessibility reader
+        assertAccessibilityTree {
+            node {
+                label = "Root"
+            }
+            node {
+                label = "Popup 1"
+            }
+            node {
+                label = "Popup 2"
+            }
+        }
+
+        topPopupFocusable.value = true
+        // Popup should react on focusable flag change
+        assertAccessibilityTree {
+            label = "Popup 2"
+        }
+
+        topPopup.value = false
+        bottomPopup.value = false
+        assertAccessibilityTree {
+            label = "Root"
+        }
+    }
+
+    @Test
+    fun testNodesCoveredByDialog() = runUIKitInstrumentedTest {
+        val showDialog = mutableStateOf(false)
+        setContentWithAccessibilityEnabled {
+            Text("Root")
+            Popup {
+                Text("Popup")
+            }
+            if (showDialog.value) {
+                Dialog(onDismissRequest = {}) {
+                    Text("Dialog")
+                }
+            }
+        }
+
+        assertAccessibilityTree {
+            node {
+                label = "Root"
+            }
+            node {
+                label = "Popup"
+            }
+        }
+
+        showDialog.value = true
+        // Dialog popup should hide content under it for accessibility reader
+        assertAccessibilityTree {
+            label = "Dialog"
+        }
+
+        showDialog.value = false
+
+        assertAccessibilityTree {
+            node {
+                label = "Root"
+            }
+            node {
+                label = "Popup"
+            }
+        }
+    }
+
+    @Test
+    fun testLayersAppearanceOrder() = runUIKitInstrumentedTest {
+        val bottomLayer = mutableStateOf(false)
+        val middleLayers = mutableStateOf(false)
+        setContentWithAccessibilityEnabled {
+            Text("Root")
+            if (bottomLayer.value) {
+                Popup(properties = PopupProperties(focusable = true)) {
+                    Text("Bottom")
+                }
+            }
+            if (middleLayers.value) {
+                Popup(properties = PopupProperties(focusable = true)) {
+                    Text("Middle 1")
+                }
+                // Non-focusable layer
+                Popup {
+                    Text("Middle 2")
+                }
+            }
+            Popup(properties = PopupProperties(focusable = true)) {
+                Text("Top")
+            }
+        }
+
+        assertAccessibilityTree {
+            label = "Top"
+        }
+
+        bottomLayer.value = true
+        // The last added layer should be on top
+        assertAccessibilityTree {
+            label = "Bottom"
+        }
+
+        middleLayers.value = true
+        // The last added layers should be on top
+        assertAccessibilityTree {
+            node {
+                label = "Middle 1"
+            }
+            node {
+                label = "Middle 2"
+            }
+        }
+    }
+}