Add changes file for Qt 5.15.0

+ f0c97814 Bump version
+ cf2ca6dc Update the Qt Quick Compiler docs with regards to resource handling
+ 58c17ea6 Use networkError instead of error
+ ea11d049 Revert "Use networkError instead of error"
+ 49591c45 Demos: request Android storage permissions when using QStandardPaths
+ 1c236912 Use Qt::SplitBehavior in preference to QString::SplitBehavior
+ 490c55ff Remove the comment about building MySQL and clarify doc
+ d17f1b97 Doc: Remove \contentspage commands
+ 0c1a0fd1 Record 5.15's updates to UCD and the public suffix list
+ dcfe75ec Update the supported platforms documentation re Visual Studio 2019
+ 9dbfb42c Doc: Remove incomplete list of development tools
+ 7634e39b WASM: Do not recommend --embedded option for emsdk
+ 5f047a35 Document minimum emsdk version for Qt 5.15
+ a86bcb6b Improve IPC documentation
+ d9b39705 Android: move and re-organize android docs to separate platforms/android
+ 5cec5e99

 Add chromium updates for 5.14 and 5.15

Change-Id: I7279d5fd014ad3c96b3d453a46492f965bc710ce
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

dist/changes-5.15.0

+Qt 5.15 introduces many new features and improvements as well as bugfixes
+over the 5.14.x series. For more details, refer to the online documentation
+included in this distribution. The documentation is also available online:
+
+https://doc.qt.io/qt-5/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.