Add changes file for 4.12.3

Change-Id: Iaea37345615c572da2bd5697e0a5d771a9168987
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

dist/changes-4.12.3.md

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+Qt Creator 4.12.3
+=================
+
+Qt Creator version 4.12.3 contains bug fixes.
+
+The most important changes are listed in this document. For a complete
+list of changes, see the Git log for the Qt Creator sources that
+you can check out from the public Git repository. For example:
+
+    git clone git://code.qt.io/qt-creator/qt-creator.git
+    git log --cherry-pick --pretty=oneline origin/v4.12.2..v4.12.3
+
+Editing
+-------
+
+* Fixed missing update of completions after cursor navigation (QTCREATORBUG-24071)
+
+### QML
+
+* Fixed line number for string literals (QTCREATORBUG-23777)
+
+### GLSL
+
+* Fixed freeze (QTCREATORBUG-24070)
+
+Projects
+--------
+
+### CMake
+
+* Fixed issue with `Add build library search path` and older CMake versions (QTCREATORBUG-23997)
+* Fixed that projects without name were considered invalid (QTCREATORBUG-24044)
+
+Debugging
+---------
+
+* Fixed QDateTime pretty printer for Qt 5.14 and newer
+* Fixed QJson pretty printer for Qt 5.15 and newer (QTCREATORBUG-23827)
+
+Platforms
+---------
+
+### Android
+
+* Fixed that installing OpenSSL for Android in the settings could delete current working directory
+  (QTCREATORBUG-24173)
+
+### MCU
+
+* Fixed issue with saving settings (QTCREATORBUG-24048)
+
+Credits for these changes go to:
+--------------------------------
+Alessandro Portale  
+André Pönitz  
+Assam Boudjelthia  
+Christian Stenger  
+Cristian Adam  
+David Schulz  
+Eike Ziller  
+Leena Miettinen  
+Tobias Hunger