AliasSeq seems to compile slightly faster with static foreach

[Jonathan M Davis]

There was a recent PR for Phobos where Seb added static to a bunch of
foreach's that used AliasSeq. It hadn't actually occurred to me that that
was legal (I've basically just been using static foreach where foreach with
AliasSeq doesn't work), but it is legal (which I suppose isn't surprising
when you think about it; I just hadn't). However, that got me to wondering
if such a change was purely aesthetic or whether it might actually have an
impact on build times - particularly since running dub test for one of my
recent projects keeps taking longer and longer. So, I added static to a
bunch of foreach's over AliasSeqs in that project to see if it would have
any effect. The result was that dub test went from about 16.5 seconds on my
system to about 15.8 seconds - and that's just by adding static to the
foreach's over AliasSeqs, not fundamentally changing what any of the code
did. That's not a huge speed up, but it's definitely something and far more
than I was expecting.

Of course, you have to be careful with such a change, because static foreach
doesn't introduce a new scope, and double braces are potentially required
where they weren't before, but given that I'd very much like to streamline
that test build, adding static to those foreach's was surprisingly
worthwhile.

Taking it a step further, I tried switching some of the static foreach's
over to using array literals, since they held values rather than types, and
that seemed to have minimal impact on the time to run dub test. However, by
switching to using std.range.only, it suddenly was taking more like 11.8
seconds. So, with a few small changes, I cut the time to run dub test down
by almost a third.

- Jonathan M Davis