Add changes file for Qt 5.12.3

+ fea4d302 Gstreamer: Set surface from renderer before creating pipeline
+ 09490d1a Doc: Fix documented QtMultimedia import
+ 935967a4 Fix compile failure with gstreamer 0.10
+ d665520e Bump version
+ 226f802f Add source url to 'decoding error' warning
+ c296df78 Fix QCameraInfo to be invalid if camera failed to find device
+ 80411380 winrt: Use highest supported resolution for camera preview/image capture
+ f4181938

 Android: Use CaptureStillImage as default capture mode

Change-Id: I2cf7a9c86b08e72ffbea9901371a40610b65eadd
Reviewed-by: Christian Strømme <christian.stromme@qt.io>