TouchControls: touch_use_crosshair, dig/place simulation refactoring (#15800)

-   get rid of simulated mouse events for digging/placing, use keyboard events
    instead
    -   consistent with other simulated events, less code, no need for a
        pointer position
    -   more correct: touch controls no longer break if you have custom
        dig/place keybindings set
-   move reading of "touch_use_crosshair" setting from Game to TouchControls

src/gui/touchcontrols.h

@@ -93,6 +93,8 @@ public:
 		return res;
 	}
 
+	bool isShootlineAvailable() { return !m_use_crosshair; }
+
 	/**
 	 * Returns a line which describes what the player is pointing at.
 	 * The starting point and looking direction are significant,
@@ -100,6 +102,9 @@ public:
 	 * the player can reach.
 	 * The line starts at the camera and ends on the camera's far plane.
 	 * The coordinates do not contain the camera offset.
+	 *
+	 * This may only be used if isShootlineAvailable returns true.
+	 * Otherwise, the normal crosshair must be used.
 	 */
 	line3d<f32> getShootline() { return m_shootline; }
 
@@ -107,7 +112,6 @@ public:
 	float getJoystickSpeed() { return m_joystick_speed; }
 
 	void step(float dtime);
-	inline void setUseCrosshair(bool use_crosshair) { m_draw_crosshair = use_crosshair; }
 
 	void setVisible(bool visible);
 	void hide();
@@ -132,6 +136,7 @@ private:
 	s32 m_button_size;
 
 	// cached settings
+	bool m_use_crosshair;
 	double m_touchscreen_threshold;
 	u16 m_long_tap_delay;
 	bool m_fixed_joystick;
@@ -143,9 +148,6 @@ private:
 	ButtonLayout m_layout;
 	void applyLayout(const ButtonLayout &layout);
 
-	// not read from a setting, but set by Game via setUseCrosshair
-	bool m_draw_crosshair = false;
-
 	std::unordered_map<u16, recti> m_hotbar_rects;
 	std::optional<u16> m_hotbar_selection = std::nullopt;
 
@@ -157,6 +159,8 @@ private:
 	 * A line starting at the camera and pointing towards the selected object.
 	 * The line ends on the camera's far plane.
 	 * The coordinates do not contain the camera offset.
+	 *
+	 * Only valid if !m_use_crosshair
 	 */
 	line3d<f32> m_shootline;
 
@@ -164,7 +168,9 @@ private:
 	size_t m_move_id;
 	bool m_move_has_really_moved = false;
 	u64 m_move_downtime = 0;
-	// m_move_pos stays valid even after m_move_id has been released.
+	// m_move_pos stays valid even after the m_move_id pointer has been
+	// released and m_pointer_pos[m_move_id] has been erased
+	// (or even overwritten by a new pointer reusing the same id).
 	v2s32 m_move_pos;
 	// This is needed so that we don't miss if m_has_move_id is true for less
 	// than one client step, i.e. press and release happen in the same step.
@@ -236,8 +242,6 @@ private:
 	// map to store the IDs and positions of currently pressed pointers
 	std::unordered_map<size_t, v2s32> m_pointer_pos;
 
-	v2s32 getPointerPos();
-	void emitMouseEvent(EMOUSE_INPUT_EVENT type);
 	TouchInteractionMode m_last_mode = TouchInteractionMode_END;
 	TapState m_tap_state = TapState::None;