graphics/qcustomplot-qt5: rename and add Qt6 flavor

[makc]

trim patch

[yuri]

misc/nn-insight/Makefile

21

I think that this and similar lines should have flavor:

libQCustomPlot-qt5.so:graphics/qcustomplot@qt5

[makc]

Add @qt5

misc/nn-insight/Makefile

21

Qt5 flavor is a default flavor, so it's noop. If we switch to Qt6 by default, than it would be needed.

[yuri]

Approved, provided that this port and all affected dependencies build successfully in poudriere.