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/ipa_proxy.cpp

@@ -159,7 +159,7 @@ std::string IPAProxy::configurationFile(const std::string &name) const
  *
  * A proxy worker's executable could be found in either the global installation
  * directory, or in the paths specified by the environment variable
- * LIBCAMERA_IPA_PROXY_PATH. This method checks the global install directory
+ * LIBCAMERA_IPA_PROXY_PATH. This function checks the global install directory
  * first, then LIBCAMERA_IPA_PROXY_PATH in order, and returns the full path to
  * the proxy worker executable that is specified by file. The proxy worker
  * executable shall have exec permission.
@@ -233,7 +233,7 @@ std::string IPAProxy::resolvePath(const std::string &file) const
  *
  * The IPAProxy can be Running, Stopped, or Stopping.
  *
- * This state provides a means to ensure that asynchronous methods are only
+ * This state provides a means to ensure that asynchronous functions are only
  * called while the proxy is running, and prevent new tasks being submitted
  * while still enabling events to complete when the IPAProxy is stopping.
  */