Initial swkbd implementation (#826)

* am: Initial swkbd implementation

Currently only implements the full screen keyboard, inline keyboard will come later.

* Remove unnecessary logging

* Miscellaneous tidy up

* am: Always pop incoming interactive session data

* am: Add a reminder to implement the full config struct

* am: Check for a max length of zero

We should only limit/truncate text when the max length is set to a non-zero value.

* Add documentation

* am: Return IStorage not available when queue is empty

We should be returning the appropriate error code when the FIFO is empty, rather than just throwing an exception and killing the emulator.

* Fix typo

* Code style changes

Ryujinx.HLE/HOS/Applets/SoftwareKeyboard/SoftwareKeyboardState.cs

@@ -0,0 +1,25 @@
+namespace Ryujinx.HLE.HOS.Applets.SoftwareKeyboard
+{
+    internal enum SoftwareKeyboardState
+    {
+        /// <summary>
+        /// swkbd is uninitialized.
+        /// </summary>
+        Uninitialized,
+
+        /// <summary>
+        /// swkbd is ready to process data.
+        /// </summary>
+        Ready,
+
+        /// <summary>
+        /// swkbd is awaiting an interactive reply with a validation status.
+        /// </summary>
+        ValidationPending,
+
+        /// <summary>
+        /// swkbd has completed.
+        /// </summary>
+        Complete
+    }
+}