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/geometry.cpp

@@ -651,7 +651,7 @@ Rectangle &Rectangle::translateBy(const Point &point)
  * \brief Calculate the intersection of this Rectangle with another
  * \param[in] bound The Rectangle that is intersected with this Rectangle
  *
- * This method calculates the standard intersection of two rectangles. If the
+ * This function calculates the standard intersection of two rectangles. If the
  * rectangles do not overlap in either the x or y direction, then the size
  * of that dimension in the result (its width or height) is set to zero. Even
  * when one dimension is set to zero, note that the other dimension may still