android: add content labels (#352)

Address content labeling warnings surfaced by pre-launch report

Updates tailscale/corp#18976

Signed-off-by: kari-ts <kari@tailscale.com>

android/src/main/java/com/tailscale/ipn/ui/view/MainView.kt

@@ -263,7 +263,7 @@ fun ExitNodeStatus(navAction: () -> Unit, viewModel: MainViewModel) {
 @Composable
 fun SettingsButton(action: () -> Unit) {
   IconButton(modifier = Modifier.size(24.dp), onClick = { action() }) {
-    Icon(Icons.Outlined.Settings, null, tint = MaterialTheme.colorScheme.onSurfaceVariant)
+    Icon(Icons.Outlined.Settings, contentDescription = "Open settings", tint = MaterialTheme.colorScheme.onSurfaceVariant)
   }
 }
 

android/src/main/java/com/tailscale/ipn/ui/view/SharedViews.kt

@@ -60,7 +60,7 @@ fun BackArrow(action: () -> Unit) {
   Box(modifier = Modifier.padding(start = 8.dp, end = 8.dp)) {
     Icon(
         Icons.AutoMirrored.Filled.ArrowBack,
-        null,
+        contentDescription = "Go back to the previous screen",
         modifier =
             Modifier.clickable(
                 interactionSource = remember { MutableInteractionSource() },