simdarray: implement (masked) setZero(Inverted)

refs #613

Signed-off-by: Matthias Kretz <kretz@kde.org>
simdarray: implement non-const operator[]

asserts that the storage_types are compatible

refs #613

Signed-off-by: Matthias Kretz <kretz@kde.org>
simdarray: implement Mask::toInt

refs #613

Signed-off-by: Matthias Kretz <kretz@kde.org>