libcamera: Rename 'method' to 'function'

Usage of 'method' to refer to member functions comes from Java. The C++
standard uses the term 'function' only. Replace 'method' with 'function'
or 'member function' through the whole code base and documentation.
While at it, fix two typos (s/backeng/backend/).

The BoundMethod and Object::invokeMethod() are left as-is here, and will
be addressed separately.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Acked-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/ipa/libipa/camera_sensor_helper.cpp

@@ -41,7 +41,7 @@ namespace ipa {
  * \brief Construct a CameraSensorHelper instance
  *
  * CameraSensorHelper derived class instances shall never be constructed
- * manually but always through the CameraSensorHelperFactory::create() method.
+ * manually but always through the CameraSensorHelperFactory::create() function.
  */
 
 /**