libcamera: v4l2_controls: Turn V4L2ControlInfoMap into a class

In preparation for extending V4L2ControlInfoMap with control idmap
support, turn it into a real class. Make it inherit from std::map<>
instead of wrapping it to keep the API simple.

V4L2ControlInfoMap is meant to be constructed with a set of control
info, and never modified afterwards. To ensure this, inherit from
std::map<> with private access specifier, and explicitly expose the
std::map<> methods that do not allow insertion or removal of elements. A
custom move assignment operator is implemented to allow efficient
construction of the V4L2ControlInfoMap.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Tested-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/libcamera/include/v4l2_controls.h

@@ -43,7 +43,21 @@ private:
 	ControlRange range_;
 };
 
-using V4L2ControlInfoMap = std::map<unsigned int, V4L2ControlInfo>;
+class V4L2ControlInfoMap : private std::map<unsigned int, V4L2ControlInfo>
+{
+public:
+	V4L2ControlInfoMap &operator=(std::map<unsigned int, V4L2ControlInfo> &&info);
+
+	using std::map<unsigned int, V4L2ControlInfo>::begin;
+	using std::map<unsigned int, V4L2ControlInfo>::cbegin;
+	using std::map<unsigned int, V4L2ControlInfo>::end;
+	using std::map<unsigned int, V4L2ControlInfo>::cend;
+	using std::map<unsigned int, V4L2ControlInfo>::at;
+	using std::map<unsigned int, V4L2ControlInfo>::empty;
+	using std::map<unsigned int, V4L2ControlInfo>::size;
+	using std::map<unsigned int, V4L2ControlInfo>::count;
+	using std::map<unsigned int, V4L2ControlInfo>::find;
+};
 
 class V4L2Control
 {