Steno combinedkeys (#12538)

* Add support for steno keys that press adjacent keys simultaniously

* Add some docs for steno combined keys

quantum/keymap_extras/keymap_steno.h

@@ -72,3 +72,21 @@ enum steno_keycodes {
     STN_ZR,
     STN__MAX = STN_ZR,  // must be less than QK_STENO_BOLT
 };
+
+#ifdef STENO_COMBINEDMAP
+enum steno_combined_keycodes
+{
+    STN_S3 = QK_STENO_COMB,
+    STN_TKL,
+    STN_PWL,
+    STN_HRL,
+    STN_FRR,
+    STN_PBR,
+    STN_LGR,
+    STN_TSR,
+    STN_DZR,
+    STN_AO,
+    STN_EU,
+    STN_COMB_MAX = STN_EU,
+};
+#endif