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/libcamera/device_enumerator.cpp

@@ -244,7 +244,7 @@ std::unique_ptr<MediaDevice> DeviceEnumerator::createDevice(const std::string &d
  *
  * Store the media device in the internal list for later matching with
  * pipeline handlers. \a media shall be created with createDevice() first.
- * This method shall be called after all members of the entities of the
+ * This function shall be called after all members of the entities of the
  * media graph have been confirmed to be initialized.
  */
 void DeviceEnumerator::addDevice(std::unique_ptr<MediaDevice> media)