tas_input: Make TasAxes enum an enum class

Prevents these values from potentially clashing with anything in other
headers.

src/input_common/drivers/tas_input.h

@@ -128,6 +128,8 @@ public:
     std::tuple<TasState, size_t, size_t> GetStatus() const;
 
 private:
+    enum class TasAxis : u8;
+
     struct TASCommand {
         u64 buttons{};
         TasAnalog l_axis{};
@@ -182,6 +184,9 @@ private:
      */
     std::string WriteCommandAxis(TasAnalog data) const;
 
+    /// Sets an axis for a particular pad to the given value.
+    void SetTasAxis(const PadIdentifier& identifier, TasAxis axis, f32 value);
+
     size_t script_length{0};
     bool is_recording{false};
     bool is_running{false};