Add TX Bolt protocol support for Stenography

Requires virtser; Allows QMK to speak the TX BOlt protocol used by stenography machines and software (such as Plover). The upside is that Plover can be configured to listen only to TX Bolt allow the keyboard to switch layers without need to enable/disable the Plover software, or to have a second non-Steno keyboard work concurrently.

quantum/process_keycode/process_steno.h

@@ -0,0 +1,12 @@
+#ifndef PROCESS_STENO_H
+#define PROCESS_STENO_H
+
+#include "quantum.h"
+
+#if defined(STENO_ENABLE) && !defined(VIRTSER_ENABLE)
+  #error "must have virtser enabled to use steno"
+#endif
+
+bool process_steno(uint16_t keycode, keyrecord_t *record);
+
+#endif