[android] port RootLayout.axml to Java

[jonathanpeppers]

dotnet trace output of dotnet new maui on a Pixel 5 shows:

178.32ms microsoft.maui.controls!Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.OnCreateView(Android.Views.LayoutInflater,Android.Views.ViewGroup,Android.OS.Bundle)
 31.05ms mono.android!Android.Views.LayoutInflater.Inflate
 16.95ms xamarin.google.android.material!Google.Android.Material.Tabs.TabLayoutMediator.Attach
  7.12ms mono.android!Android.Views.View.FindViewById(int)
  2.42ms xamarin.google.android.material!Google.Android.Material.Tabs.TabLayoutMediator.ITabConfigurationStrategyInvoker.n_OnConfigureTab_Lcom_google_android_material_tabs_TabLayout_Tab_I(intptr,intptr,intptr,int)
  1.22ms mono.android!Android.Views.View.set_OverScrollMode(Android.Views.OverScrollMode)
  1.20ms xamarin.androidx.viewpager2!AndroidX.ViewPager2.Widget.ViewPager2.set_Adapter
  1.16ms xamarin.google.android.material!Google.Android.Material.Tabs.TabLayoutMediator..ctor

A lot of the time spent is inflating RootLayout.axml and calling
FindViewById to get views from the inflated layout.

Instead, we can port this to 5 Java methods that return each of the
views directly. This avoids XML parsing, as well as reduces C# to Java
interop.

We can also move some calls that are in C# to Java, such as:

_viewPager.Id = AView.GenerateViewId();
_viewPager.Adapter = new ShellFragmentStateAdapter(shellSection, ChildFragmentManager, pagerContext);
_viewPager.OverScrollMode = OverScrollMode.Never;
_viewPager.RegisterOnPageChangeCallback(new ViewPagerPageChanged(this));
new TabLayoutMediator(_tablayout, _viewPager, this)
    .Attach();

Moving these to the Java side, will reduce ~6 interop calls from C# to Java.

Lastly, I found some repeated calls to SectionController.GetItems()
(which copies a new ReadonlyCollection) that we could store in a
local variable instead.

After these changes, dotnet trace output changes to:

130.29ms Microsoft.Maui.Controls!Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.OnCreateView(Android.Views.LayoutInflater,Android.Views.ViewGroup,Android.OS.Bundle)
 28.47ms Microsoft.Maui!Microsoft.Maui.ViewHelper.CreateViewPager(Android.Content.Context,AndroidX.CoordinatorLayout.Widget.CoordinatorLayout,Google.Android.Material.Tabs.TabLayout,Google.Android.Material.Tabs.TabLayoutMediator/ITabConfigurationStrategy,AndroidX.ViewPager2.Adapter.FragmentStateAd
  8.86ms Microsoft.Maui!Microsoft.Maui.ViewHelper.CreateTabLayout(Android.Content.Context,Google.Android.Material.AppBar.AppBarLayout,int)
  5.29ms Microsoft.Maui!Microsoft.Maui.ViewHelper.CreateCoordinatorLayout(Android.Content.Context)
  2.65ms Microsoft.Maui!Microsoft.Maui.ViewHelper.CreateMaterialToolbar(Android.Content.Context,Google.Android.Material.AppBar.AppBarLayout,int,int)
  2.58ms Microsoft.Maui!Microsoft.Maui.ViewHelper.CreateAppBar(Android.Content.Context,int,AndroidX.CoordinatorLayout.Widget.CoordinatorLayout)

Which is a ~48ms improvement for dotnet new maui.

[jonathanpeppers]

I think the tabs on the podcast app are testing these changes:

[jonathanpeppers]

@PureWeen I was wondering about this, do I need to test a Shell flyout for these changes?