Update Qt5 to 5.15

This is a major upgrade of the Qt libraries [1], [2].

• People that use upgrading mechanisms with incomplete dependency handling (portmaster & Co) should make sure to manually remove the existing Qt packages to guarantee a safe upgrade. Keep in mind, that Qt does not like if you have an incomplete upgrade.

• This version of Qt drops support for OpenSSL 1.0 -- this means that there won't be any binary packages for Qt5 provided by the FreeBSD package builders for FreeBSD 11.x anymore -- and the same for *all* the ports depending on net/qt5-network [3]. If you cannot upgrade to a more recent FreeBSD version (12.x, 13.x), you will need to build Qt5 from ports while switching to an SSL implementation from ports.

Big thanks are due for

• kai@ for updating webengine (also mikael@)
• Felix Palmen for providing LibreSSL support patches
• adridg@ and lbartoletti@ for helping me fix the fallout

[1] https://www.qt.io/blog/qt-5.15-released
[2] https://wiki.qt.io/New_Features_in_Qt_5.15
[3] https://www.freshports.org/net/qt5-network

PR: 247010
Exp-run by: antoine