This updates is_windows_subsystem_for_linux() to take a WSL version to test for
(any, v1, or v2) and returns the boolean result depending on the system. I've
benchmarked and when running on regular Linux, this is still just as fast as the
previous binary check; it's only when it's WSL that this takes about 20ns
longer to figure out which variant.
Note that older WSLv2 kernels had a `-microsoft-standard` suffix while newer
ones appear to have a `-microsoft-standard-WSL2` suffix, so we make sure to test
for the least common denominator. (It doesn't matter to us, but note that newer
WSLv2 kernels have four dots in the version string!)
WSL workarounds pertaining to the default Windows terminal or executable
behavior of win32 binaries under a WSL shell are extended to WSLv2 while those
specific to oddities in kernel behavior are confined to WSLv1 only. (It
technically wouldn't hurt to extend them to WSLv2 but there's no good reason to
do so, either.)
