Hand Android's own focus back to the terminal after an accessory key

Focusable=false was only ever half the fix, and its remark now says so:
Avalonia's focus stays on the NativeWebView, but the touch that presses
a key still hands Android's native focus to Avalonia's input view — the
platform moves it before Avalonia decides anything. The WebView's input
connection dies with it, the keyboard swaps to its no-input layout, and
the inset churn parks it over the very row that was tapped.

Each key now returns that focus once its byte is on the wire, through a
sibling of SoftKeyboard that walks the decor view to the one WebView
this application has. Free when nothing moved. Check 11.10a is the
phone-in-hand proof.

src/DodoSSH.Client.Android/Platform/TerminalFocus.cs

@@ -0,0 +1,64 @@
+using global::Android.Views;
+
+namespace DodoSSH.Client.Android.Platform;
+
+/// <summary>
+/// Hands native focus back to the terminal's WebView after Avalonia chrome took it.
+/// </summary>
+/// <remarks>
+/// <para>
+/// <b>The sibling of <see cref="SoftKeyboard"/>, and it exists for the same reason that one does:</b> the
+/// keyboard over a terminal belongs to the WebView's own native view, which Avalonia's focus manager does
+/// not own. The accessory row's keys are already <c>Focusable=false</c> — see TerminalScreen — so Avalonia's
+/// idea of focus never leaves the terminal when one is tapped. What still moves is <em>Android's</em>: the
+/// tap lands on Avalonia's own input view, which is focusable-in-touch-mode because Avalonia's text boxes
+/// need it to be, and the platform hands that view focus on the way to delivering the touch. The WebView's
+/// input connection dies with its focus, the keyboard swaps to the layout it shows an editor that takes no
+/// text, and the inset churn that follows can leave it sitting on top of the very row that was tapped.
+/// </para>
+/// <para>
+/// So each accessory key hands focus straight back once its byte is on the wire. The page inside the
+/// WebView never noticed anything — its own DOM focus never moved — so regaining native focus re-establishes
+/// the same input connection and the keyboard settles back to what it was. Skipped when the WebView is still
+/// focused, which makes the call free on any platform arrangement where the steal never happened.
+/// </para>
+/// <para>
+/// Found by walking the decor view rather than asked of the <c>NativeWebView</c> control, because the
+/// control does not expose its platform child and this application only ever has the one WebView — the
+/// walk's first match is necessarily the terminal. Every step is allowed to be absent, exactly as
+/// <see cref="SoftKeyboard.Hide"/>'s are: no activity while backgrounded, no WebView while the terminal
+/// surface has never been shown, and nothing to do in either case.
+/// </para>
+/// </remarks>
+internal static class TerminalFocus
+{
+    public static void Return()
+    {
+        if (PhoneEnvironment.CurrentActivity?.Window?.DecorView is not ViewGroup decor)
+        {
+            return;
+        }
+
+        if (FindWebView(decor) is { IsFocused: false } webView)
+        {
+            webView.RequestFocus();
+        }
+    }
+
+    private static View? FindWebView(ViewGroup parent)
+    {
+        for (var i = 0; i < parent.ChildCount; i++)
+        {
+            switch (parent.GetChildAt(i))
+            {
+                case global::Android.Webkit.WebView webView:
+                    return webView;
+
+                case ViewGroup child when FindWebView(child) is { } found:
+                    return found;
+            }
+        }
+
+        return null;
+    }
+}