Select the last tab and update selection after deleting the current tab (#4697)

Task/Issue URL:
https://app.asana.com/0/1202552961248957/1202148076467684/f

### Description
This PR selects the last tab in the list after the currently-selected
tab is deleted. This fixes the behaviour when no tab was selected and
when the user went back to the browser, the first tab was shown.

### Steps to test this PR

1. Create at least 3 tabs (with the last tab being selected)
2. Delete the last (selected) tab
3. Notice the tab is removed and the last of the remaining tab is
selected
4. Tap on `Undo`
5. Notice the previous tab is shown and selected again
6. Delete the selected tab again
7. Tap on the back button
8. Notice the correct tab is shown

### UI changes

[Screen_recording_20240626_151442.webm](https://github.com/duckduckgo/Android/assets/1522856/2ae2fe33-275b-4eb8-a33c-62b647715d09)

Author: 0nko

app/src/main/java/com/duckduckgo/app/tabs/db/TabsDao.kt

@@ -93,7 +93,7 @@ abstract class TabsDao {
         if (selectedTab() != null) {
             return
         }
-        firstTab()?.let {
+        lastTab()?.let {
             insertTabSelection(TabSelectionEntity(tabId = it.tabId))
         }
     }

app/src/main/java/com/duckduckgo/app/tabs/ui/TabSwitcherActivity.kt

@@ -148,8 +148,18 @@ class TabSwitcherActivity : DuckDuckGoActivity(), TabSwitcherListener, Coroutine
     }
 
     private fun configureObservers() {
-        viewModel.tabs.observe(this) {
-            render(it)
+        viewModel.tabs.observe(this) { tabs ->
+            render(tabs)
+
+            val noTabSelected = tabs.none { it.tabId == tabGridItemDecorator.selectedTabId }
+            if (noTabSelected && tabs.isNotEmpty()) {
+                updateTabGridItemDecorator(tabs.last())
+            }
+        }
+        viewModel.activeTab.observe(this) { tab ->
+            if (tab != null && tab.tabId != tabGridItemDecorator.selectedTabId && !tab.deletable) {
+                updateTabGridItemDecorator(tab)
+            }
         }
         viewModel.deletableTabs.observe(this) {
             if (it.isNotEmpty()) {

app/src/main/java/com/duckduckgo/app/tabs/ui/TabSwitcherViewModel.kt

@@ -40,6 +40,7 @@ class TabSwitcherViewModel @Inject constructor(
 ) : ViewModel() {
 
     var tabs: LiveData<List<TabEntity>> = tabRepository.liveTabs
+    val activeTab = tabRepository.liveSelectedTab
     var deletableTabs: LiveData<List<TabEntity>> = tabRepository.flowDeletableTabs.asLiveData(
         context = viewModelScope.coroutineContext,
     )