Functions in AK/GenericShorthands used pass-by-value which results in
copying values when calling those functions. This could be expensive
for complex types. To optimize performance, we switch the functions to
use forwarding references.
This patch adds the `USING_AK_GLOBALLY` macro which is enabled by
default, but can be overridden by build flags.
This is a step towards integrating Jakt and AK types.