Introduce EdgeToEdgeActivityContent

I am refreshing our Compose docs and http://go/sysui-compose-docs#activity
striked me as too complicated.

Bug: 230828788
Test: Manual
Change-Id: I1744d5dadf6052e704788107f3450fa0f0582317

packages/SystemUI/compose/core/src/com/android/compose/activity/EdgeToEdgeActivitContent.kt

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2023 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 com.android.compose.activity
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.material3.LocalContentColor
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.contentColorFor
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.runtime.DisposableEffect
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import com.android.compose.rememberSystemUiController
+import com.android.compose.theme.PlatformTheme
+
+/** Scaffolding for an edge-to-edge activity content. */
+@Composable
+fun EdgeToEdgeActivityContent(
+    modifier: Modifier = Modifier,
+    content: @Composable () -> Unit,
+) {
+    // Make the status and navigation bars transparent, ensuring that the status bar icons are dark
+    // when the theme is light and vice-versa.
+    val systemUiController = rememberSystemUiController()
+    val isDarkTheme = isSystemInDarkTheme()
+    val useDarkIcons = !isDarkTheme
+    DisposableEffect(systemUiController, useDarkIcons) {
+        systemUiController.setSystemBarsColor(
+            color = Color.Transparent,
+            darkIcons = useDarkIcons,
+        )
+        onDispose {}
+    }
+
+    PlatformTheme(isDarkTheme) {
+        val backgroundColor = MaterialTheme.colorScheme.background
+        Box(modifier.fillMaxSize().background(backgroundColor)) {
+            CompositionLocalProvider(LocalContentColor provides contentColorFor(backgroundColor)) {
+                content()
+            }
+        }
+    }
+}