Add changes file for Qt 5.11.3

+ 43403038cf Update bundled libtiff to version 4.0.10
+ 0c8d172cf3 Update bundled libwebp to version 1.0.1
+ 7cfe47a8fe TGA handler: check for out of range image size
+ 80017a1c7f Bundled libtiff: add a number of security-related upstream patches
+ 8455ab6cb2 tiffhandler: improve stripsize
+ 2f61f40118 Bump version

Change-Id: If31999c0f727ce8b73e5ffb35e247d1106011bb9
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

dist/changes-5.11.3

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+Qt 5.11.3 is a bug-fix release. It maintains both forward and backward
+compatibility (source and binary) with Qt 5.11.0 through 5.11.2.
+
+For more details, refer to the online documentation included in this
+distribution. The documentation is also available online:
+
+http://doc.qt.io/qt-5/index.html
+
+The Qt version 5.11 series is binary compatible with the 5.10.x series.
+Applications compiled for 5.10 will continue to run with 5.11.
+
+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.
+
+
+****************************************************************************
+*                              Third-party Code                            *
+****************************************************************************
+
+ - Bundled libtiff was updated to version 4.0.10
+ - Bundled libwebp was updated to version 1.0.1
+
+****************************************************************************
+*                                   TIFF                                   *
+****************************************************************************
+
+ - Improved strip size setting when writing, for better compression