Added tetra rx ext app (#3257)

firmware/application/external/tetra_rx/tetra_descrambler.hpp

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <stdint.h>
+#include "tetra_bits.hpp"
+
+namespace ui::external_app::tetra_rx {
+
+class Descrambler {
+   public:
+    static constexpr uint32_t SCRAMB_INIT_BSCH = 0x00000003;
+
+    static void descramble(
+        BitVector& bits,
+        uint32_t init = SCRAMB_INIT_BSCH);
+
+    static void generate(
+        uint32_t init,
+        uint8_t* sequence,
+        size_t bits);
+
+    static uint32_t dmo_scramb_init(
+        uint32_t mni,
+        uint32_t src);
+};
+
+}  // namespace ui::external_app::tetra_rx