android/tv: fix focus highlighting on back buttons

updates tailscale/corp#26199

The back buttons would not highlight properly when
they are focussed on Android TV.  This pulls in what
was implemented for the Avatar.

Some small tweaks to the action animation so that it
has a nice radius instead of a square box.

Signed-off-by: Jonathan Nobels <jonathan@tailscale.com>

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

@@ -42,7 +42,7 @@ fun Avatar(
     action: (() -> Unit)? = null,
     isFocusable: Boolean = false
 ) {
-  var isFocused = remember { mutableStateOf(false) }
+  val isFocused = remember { mutableStateOf(false) }
   val focusManager = LocalFocusManager.current
 
   // Outer Box for the larger focusable and clickable area

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

@@ -4,6 +4,7 @@
 package com.tailscale.ipn.ui.view
 
 import androidx.annotation.StringRes
+import androidx.compose.foundation.background
 import androidx.compose.foundation.clickable
 import androidx.compose.foundation.focusable
 import androidx.compose.foundation.interaction.MutableInteractionSource
@@ -11,6 +12,7 @@ import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.RowScope
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.automirrored.filled.ArrowBack
 import androidx.compose.material.icons.filled.CheckCircle
@@ -24,10 +26,14 @@ import androidx.compose.material3.TopAppBar
 import androidx.compose.material3.ripple
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
 import androidx.compose.ui.focus.FocusRequester
 import androidx.compose.ui.focus.focusRequester
+import androidx.compose.ui.focus.onFocusChanged
+import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.unit.dp
 import com.tailscale.ipn.ui.theme.topAppBar
@@ -77,23 +83,32 @@ fun Header(
 
 @Composable
 fun BackArrow(action: () -> Unit, focusRequester: FocusRequester) {
-  val modifier =
+  val isFocused = remember { mutableStateOf(false) }
+
+  val boxModifier =
       if (isAndroidTV()) {
         Modifier.focusRequester(focusRequester)
-            .focusable() // Ensure the composable can receive focus
+            .clip(CircleShape) // Ensure both the focus and click area are circular
+            .background(
+                if (isFocused.value) MaterialTheme.colorScheme.surface else Color.Transparent,
+            )
+            .onFocusChanged { focusState -> isFocused.value = focusState.isFocused }
+            .focusable()
       } else {
         Modifier
       }
 
-  Box(modifier = modifier.padding(start = 8.dp, end = 8.dp)) {
+  val iconModifier =
+      Modifier.clickable(
+          interactionSource = remember { MutableInteractionSource() },
+          indication = ripple(bounded = false, radius = 24.dp),
+          onClick = action)
+
+  Box(modifier = boxModifier.padding(start = 8.dp, end = 8.dp)) {
     Icon(
         Icons.AutoMirrored.Filled.ArrowBack,
         contentDescription = "Go back to the previous screen",
-        modifier =
+        modifier = iconModifier)
-            Modifier.clickable(
-                interactionSource = remember { MutableInteractionSource() },
-                indication = ripple(bounded = true),
-                onClick = action))
   }
 }