gui2/text_box: Implement I-beam cursor

This is a backport to 1.14 of multiple commits from master:

 * gui2/text_box: Implement I-beam cursor
   d7f2595393
 * Don't forcefully disable colour cursors
   fc04268aa4
 * Set the I-beam cursor's hotspot properly
   c31047af47

This cursor is active when the widget has the mouse focus. You know,
like textboxes are wont to do anywhere else. Took long enough, although
there was an interaction issue with tooltips fixed in the previous
commit.

I still need to figure out how to make this work with GUI1 textboxes
(e.g. in-game console).

The colour version of the cursor was kindly provided by LordBob, and the
B&W version is my own.

src/cursor.cpp

@@ -55,6 +55,7 @@ std::array<cursor_data, cursor::NUM_CURSORS> available_cursors {{
 #ifdef __APPLE__
 	{ nullptr, boost::indeterminate, "normal.png",          "normal.png",      0, 0  },
 	{ nullptr, boost::indeterminate, "wait-alt.png",        "wait.png",        0, 0  },
+	{ nullptr, boost::indeterminate, "ibeam.png",           "ibeam.png",       14, 14 },
 	{ nullptr, boost::indeterminate, "move.png",            "move.png",        0, 0  },
 	{ nullptr, boost::indeterminate, "attack.png",          "attack.png",      0, 0  },
 	{ nullptr, boost::indeterminate, "select.png",          "select.png",      0, 0  },
@@ -64,6 +65,7 @@ std::array<cursor_data, cursor::NUM_CURSORS> available_cursors {{
 #else
 	{ nullptr, boost::indeterminate, "normal.png",      "normal.png",      0, 0  },
 	{ nullptr, boost::indeterminate, "wait.png",        "wait.png",        0, 0  },
+	{ nullptr, boost::indeterminate, "ibeam.png",       "ibeam.png",       14, 14 },
 	{ nullptr, boost::indeterminate, "move.png",        "move.png",        0, 0  },
 	{ nullptr, boost::indeterminate, "attack.png",      "attack.png",      0, 0  },
 	{ nullptr, boost::indeterminate, "select.png",      "select.png",      0, 0  },

src/cursor.hpp

@@ -27,7 +27,7 @@ struct manager
 	~manager();
 };
 
-enum CURSOR_TYPE { NORMAL, WAIT, MOVE, ATTACK, HYPERLINK, MOVE_DRAG, ATTACK_DRAG, NO_CURSOR, NUM_CURSORS };
+enum CURSOR_TYPE { NORMAL, WAIT, IBEAM, MOVE, ATTACK, HYPERLINK, MOVE_DRAG, ATTACK_DRAG, NO_CURSOR, NUM_CURSORS };
 
 /**
  * Use the default parameter to reset cursors.

src/gui/widgets/text_box_base.cpp

@@ -16,6 +16,7 @@
 
 #include "gui/widgets/text_box_base.hpp"
 
+#include "cursor.hpp"
 #include "desktop/clipboard.hpp"
 #include "gui/core/log.hpp"
 #include "gui/core/timer.hpp"
@@ -72,6 +73,7 @@ text_box_base::text_box_base(const implementation::builder_styled_widget& builde
 text_box_base::~text_box_base()
 {
 	toggle_cursor_timer(false);
+	update_mouse_cursor(false);
 }
 
 void text_box_base::set_active(const bool active)
@@ -670,6 +672,8 @@ void text_box_base::signal_handler_mouse_enter(const event::ui_event event,
 		set_state(HOVERED);
 	}
 
+	update_mouse_cursor(true);
+
 	handled = true;
 }
 
@@ -682,6 +686,23 @@ void text_box_base::signal_handler_mouse_leave(const event::ui_event event,
 		set_state(ENABLED);
 	}
 
+	update_mouse_cursor(false);
+
 	handled = true;
 }
+
+void text_box_base::update_mouse_cursor(bool enable)
+{
+	// Someone else may set the mouse cursor for us to something unusual (e.g.
+	// the WAIT cursor) so we ought to mess with that only if it's set to
+	// NORMAL or IBEAM.
+
+	if(enable && cursor::get() == cursor::NORMAL) {
+		cursor::set(cursor::IBEAM);
+	} else if(!enable && cursor::get() == cursor::IBEAM) {
+		cursor::set(cursor::NORMAL);
+	}
+}
+
+
 } // namespace gui2

src/gui/widgets/text_box_base.hpp

@@ -289,6 +289,8 @@ private:
 
 	virtual void reset_cursor_state();
 
+	void update_mouse_cursor(bool enable);
+
 	/**
 	 * Current state of the widget.
 	 *