Add changes file for Qt 5.12.10

Pick-to: dev 5.15 5.12
Change-Id: I15554d4f7878f89c15dbd22175aee902086b938f
Reviewed-by: Jani Heikkinen <jani.heikkinen@qt.io>

dist/changes-5.12.10

+Qt 5.12.10 is a bug-fix release. It maintains both forward and backward
+compatibility (source and binary) with Qt 5.12.9.
+
+For more details, refer to the online documentation included in this
+distribution. The documentation is also available online:
+
+  https://doc.qt.io/qt-5.12/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.
+
+****************************************************************************
+*                   Important Behavior Changes                             *
+****************************************************************************
+
+****************************************************************************
+*                          Library                                         *
+****************************************************************************
+
+