shims: correct `_dispatch_uptime` for Windows
shims: correct `_dispatch_uptime` for Windows

This should use `QueryUnbiasedInterruptTime`  `QueryPerformanceCounter`
is roughly in units of of TSC frequency.  We would need to use
`QueryPerformanceFrequency` to convert that into nanoseconds.
Additionally, `QueryPerformanceCounter` includes time spent during
suspend, which is not what is desired.  Switch to
`QueryUnbiasedInterruptTime` to get something close to `CLOCK_MONOTONIC`
on Linux.

apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch