Add changes file for Qt 5.15.2

- e02d4e57e1 Add changes file for Qt 5.15.1
+ d4e82a2936 Fix qt_attribution.json files by replacing newlines with \n escapes
+ 93ae552319 Bump version
+ 1cce99ccb1 TGA Plugin: print error message when tga could not be load
+ dd8edc701b Add changes file for Qt 5.12.10

Change-Id: I46b6b8a6172a3b1dca8a28af7fe13d122d7e076a
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>
(cherry picked from commit ceaf64a82e)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

dist/changes-5.15.2

@@ -0,0 +1,20 @@
+Qt 5.15.2 is a bug-fix release. It maintains both forward and backward
+compatibility (source and binary) with Qt 5.15.1.
+
+For more details, refer to the online documentation included in this
+distribution. The documentation is also available online:
+
+  https://doc.qt.io/qt-5.15/index.html
+
+The Qt version 5.15 series is binary compatible with the 5.14.x series.
+Applications compiled for 5.14 will continue to run with 5.15.
+
+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.
+
+ - This release contains only minor code improvements.