Add changes file for Qt 5.12.1

+ 4d57f6bc QtQuick: Fix & clean up alarms.pro
+ 113e24a5 Doc: Add brief section to "Qt for QNX", "Qt for VxWorks"
+ ec6883bd Doc: Remove broken link from iOS documentation
+ 9c8b6088 Bump version
+ 9aec0395 Make example code in Qt documentation also available under BSD-3-clause
+ b6a5aff9 Improve the exception safety code sample
+ 144395f0 Fix the usage of the ret variable in the exception safety code sample
+ 66bddfb5 Add changes file for Qt 5.11.3
+ 4db2e07f Doc: Document Qt Quick WebGL plugin license
+ a58fa967 Doc: Remove obsolete build instructions for Qt Quick WebGL plugin
+ 0a474628 winrt: Update winrtrunner's help output
+ 8f7c4db0 Clarify target platforms of winrt port
+ c162c4b5 windows: Fix origin of environment setup script
+ 9d889327 Doc: Replace Controls 1 and MouseArea references
+ 3361d004 Doc: Change the depends order in the doc config
+ ec479952 remove references to bundled xkbcommon
+ 10b3f2c1 macOS: improve quit menu item documentation
+ bfe54113

 Bump version

Change-Id: I63e1c88a718757a55904c5a0f4358aa651e5a40c
Reviewed-by: Topi Reiniö <topi.reinio@qt.io>