meta-qt5: update layer

Pull in latest merged content from upstream/warrior &
update Qt to latest content in 5.12.4 branch.

Changelog:
c96f9b3 qt5: update submodules
baf9b8e Merge remote-tracking branch 'qtyocto/upstream/warrior' into 5.12

Task-number: QTBUG-75966
Change-Id: I92363cc8e020024d465f342b06b6f33eab2c027a
Reviewed-by: Samuli Piippo <samuli.piippo@qt.io>