bug(windows): Keyman32 can leak some memory in multiple processes when Keyman exits

When Keyman shuts down and its hooks are unhooked, keyman32 and keyman64 are detached from each process. In this scenario, it appears we don't necessarily receive a DLL_THREAD_DETACH from every thread for which we received a DLL_THREAD_ATTACH, and so we can leak memory for those threads.

Low priority, because it's a small amount of memory (a few kb) and not otherwise detrimental.

_Originally posted by @jahorton in https://github.com/keymanapp/keyman/pull/2297_