Add changes file for Qt 5.12.3

+ 4b0d658f47 Bump version
+ 0989f6aa2d tiff handler: fix compilation failure
+ 434aa248ad Heic handler: fix orientation and other image properties

Change-Id: Icaffd1c0351fa5e816f93c79da1de55ea7f577e5
Reviewed-by: Liang Qi <liang.qi@qt.io>

dist/changes-5.12.3

@@ -0,0 +1,31 @@
+Qt 5.12.3 is a bug-fix release. It maintains both forward and backward
+compatibility (source and binary) with Qt 5.12.0 through 5.12.2.
+
+For more details, refer to the online documentation included in this
+distribution. The documentation is also available online:
+
+https://doc.qt.io/qt-5/index.html
+
+The Qt version 5.12 series is binary compatible with the 5.11.x series.
+Applications compiled for 5.11 will continue to run with 5.12.
+
+Some of the changes listed in this file include issue tracking numbers
+corresponding to tasks in the Qt Bug Tracker:
+
+https://bugreports.qt.io/
+
+Each of these identifiers can be entered in the bug tracker to obtain more
+information about a particular change.
+
+****************************************************************************
+*                          HEIC (macOS/iOS)                                *
+****************************************************************************
+
+ - Support for Size and Transformation image properties have been
+   added, so these can be queried through QImageReader prior to
+   reading the image. Automatic transformation is enabled, so images
+   that are stored rotated will by default be transformed to normal
+   orientation on reading.
+
+ - Read images will have their resolution QImage::dotsPerMeterX()/Y()
+   set according to the values in the file.