[GAR] Add focus highlight state for toolbar buttons

We have hovered and pressed highlight states defined for toolbar buttons
but not one for focused state that is used on keyboard navigation.

This CL adds a focused state similar to the hovered state that will make
the focus highlight visible during keyboard navigation.

Bug: 401309669
Change-Id: Id090e6ae1596c41e087d145f122e975d6dde7c57
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6330251
Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Reviewed-by: Sirisha Kavuluru <skavuluru@google.com>
Commit-Queue: Aishwarya Rajesh <aishwaryarj@google.com>
Cr-Commit-Position: refs/heads/main@{#1429176}

components/browser_ui/styles/android/java/res/color/toolbar_button_highlight_color.xml

@@ -9,6 +9,10 @@ found in the LICENSE file.
       android:state_hovered="true"
       android:alpha="0.08"
       android:color="?attr/colorOnSurface" />
+  <item
+      android:state_focused="true"
+      android:alpha="0.08"
+      android:color="?attr/colorOnSurface" />
   <item
       android:state_pressed="true"
       android:alpha="0.12"