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/android/jpeg/exif.cpp

@@ -40,7 +40,7 @@ enum class _ExifTag {
  *
  * Calls to generate() must check the return code to determine if any error
  * occurred during the construction of the Exif data, and if successful the
- * data can be obtained using the data() method.
+ * data can be obtained using the data() function.
  */
 Exif::Exif()
 	: valid_(false), data_(nullptr), order_(EXIF_BYTE_ORDER_INTEL),