[fenix] For https://github.com/mozilla-mobile/fenix/issues/13427 - Disable the "selected tab" decoration when in Multiselect

Selecting a tab while in Multiselect would add a different decoration to the one
already set for the last tab opened and this would confuse users.
Let's avoid this.

app/src/main/java/org/mozilla/fenix/tabtray/FenixTabsAdapter.kt

@@ -59,13 +59,22 @@ class FenixTabsAdapter(
     override fun onBindViewHolder(
         holder: TabViewHolder,
         position: Int,
-        payloads: MutableList<Any>
+        payloads: List<Any>
     ) {
         if (payloads.isNullOrEmpty()) {
             onBindViewHolder(holder, position)
             return
         }
 
+        // Having non-empty payloads means we have to make a partial update.
+        // This currently only happens when changing between the Normal and MultiSelect modes
+        // when we want to either show the last opened tab as selected (default) or hide this ui decorator.
+        if (mode is TabTrayDialogFragmentState.Mode.Normal) {
+            super.onBindViewHolder(holder, position, listOf(PAYLOAD_HIGHLIGHT_SELECTED_ITEM))
+        } else {
+            super.onBindViewHolder(holder, position, listOf(PAYLOAD_DONT_HIGHLIGHT_SELECTED_ITEM))
+        }
+
         holder.tab?.let { showCheckedIfSelected(it, holder.itemView) }
     }
 
@@ -133,6 +142,11 @@ class FenixTabsAdapter(
         tabsList = recyclerView
     }
 
+    override fun isTabSelected(tabs: Tabs, position: Int): Boolean {
+        return mode is TabTrayDialogFragmentState.Mode.Normal &&
+                tabs.selectedIndex == position
+    }
+
     private fun showCheckedIfSelected(tab: Tab, view: View) {
         val shouldBeChecked =
             mode is TabTrayDialogFragmentState.Mode.MultiSelect && selectedItems.contains(tab)

app/src/main/java/org/mozilla/fenix/tabtray/TabTrayViewHolder.kt

@@ -227,10 +227,9 @@ class TabTrayViewHolder(
             .take(MAX_URI_LENGTH)
     }
 
-    @VisibleForTesting
+    override fun updateSelectedTabIndicator(showAsSelected: Boolean) {
-    internal fun updateSelectedTabIndicator(isSelected: Boolean) {
         if (itemView.context.settings().gridTabView) {
-            itemView.tab_tray_grid_item.background = if (isSelected) {
+            itemView.tab_tray_grid_item.background = if (showAsSelected) {
                 AppCompatResources.getDrawable(itemView.context, R.drawable.tab_tray_grid_item_selected_border)
             } else {
                 null
@@ -238,7 +237,7 @@ class TabTrayViewHolder(
             return
         }
 
-        val color = if (isSelected) {
+        val color = if (showAsSelected) {
             R.color.tab_tray_item_selected_background_normal_theme
         } else {
             R.color.tab_tray_item_background_normal_theme