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/framebuffer_allocator.cpp

@@ -77,7 +77,7 @@ FrameBufferAllocator::~FrameBufferAllocator()
  * stopped, and the stream shall be part of the active camera configuration.
  *
  * Upon successful allocation, the allocated buffers can be retrieved with the
- * buffers() method.
+ * buffers() function.
  *
  * \return The number of allocated buffers on success or a negative error code
  * otherwise
@@ -137,7 +137,7 @@ int FrameBufferAllocator::free(Stream *stream)
  * \brief Retrieve the buffers allocated for a \a stream
  * \param[in] stream The stream to retrieve buffers for
  *
- * This method shall only be called after successfully allocating buffers for
+ * This function shall only be called after successfully allocating buffers for
  * \a stream with allocate(). The returned buffers are valid until free() is
  * called for the same stream or the FrameBufferAllocator instance is destroyed.
  *