[libcxx] [ci] Add a Windows CI configuration for a statically linked libc++

On Windows, static vs DLL linking affects details in quite a few
cases, so it's good to have coverage for both cases.

Testing with static linking also increases coverage for a number of
cases and individual checks that have had to be waived for the DLL
case, and allows testing libc++experimental, increasing the number
of test cases actually executed by 180 (176 new tests from
libc++experimental and 4 ones that are XFAIL windows-dll).

Also drop the "generic-" prefix from these configuration names, as
they're perhaps not what the "generic" prefix intended originally
in the other generic-posix configurations.

Differential Revision: https://reviews.llvm.org/D101565