dev-qt/qtlocation: Add USE-DEPEND on dev-qt/qtpositioning[qml]

dev-qt/qtlocation: Add USE-DEPEND on dev-qt/qtpositioning[qml]

For usage of QtPositioningQuick.

While location-labs-plugin is optional, declarativemaps is built and depends on
QtPositioningQuick unconditionally. It is probably for this reason that ${PN}
already unconditionally depends on dev-qt/qtdeclarative, so making the plugin
optional would save us nothing.

Bug: https://bugs.gentoo.org/669608
Reported-by: Toralf Förster <toralf@gentoo.org>
Thanks-to: Jimi Huotari <chiitoo@gentoo.org>
Thanks-to: Iade Gesso <iade.gesso@gmail.com>
Package-Manager: Portage-2.3.52, Repoman-2.3.12
Signed-off-by: Andreas Sturmlechner <asturm@gentoo.org>