This replaces boost::thread and most mutexes and condition variables with
std equivalents. It also adds support for std lock types to the strictest_lock
type trait.
This significantly, although not completely, reduces the dependency on
Boost.Thread.
Refs https://github.com/boostorg/log/issues/232.
C++20 removed argument type typedefs in standard function objects, which made
it impossible to deduce the attribute value type from the standard function
objects. This caused compilation errors with VS2022 in C++20 mode.
