STL: Consider cleaning up and numbering static_assert messages

MSVC's compiler warnings and errors are numbered. Somewhat recently, we started numbering the STL's deprecation warnings. These unique numbers are searchable (and can be documented, in theory):

https://github.com/microsoft/STL/blob/6b0238d7035236af0f81917262691db701e70fe3/stl/inc/yvals_core.h#L676-L681

However, we haven't been numbering our static_assert messages. We have two numbered #error messages, and that's it:

https://github.com/microsoft/STL/blob/6b0238d7035236af0f81917262691db701e70fe3/stl/inc/yvals_core.h#L425-L431

Our static_assert messages are sometimes detailed:

https://github.com/microsoft/STL/blob/6b0238d7035236af0f81917262691db701e70fe3/stl/inc/type_traits#L22-L24

And sometimes not:

https://github.com/microsoft/STL/blob/6b0238d7035236af0f81917262691db701e70fe3/stl/inc/type_traits#L1464-L1466

We should consider cleaning up our static_assert messages to be uniformly detailed (with Standardese citations when possible), and numbering them. The questions that we need to answer are:

• What numbers should we use? My initial thought is to continue imitating the compiler:
  • STL1000 series for fatal errors (e.g. using an intolerably old compiler is a configuration error that needs to be fixed before dealing with anything else)
  • STL2000 series (eventually STL3000 series) for ordinary errors
  • STL4000 series (eventually STL5000 series) for warnings
• How do we ensure that numbers are uniquely used, and never reused? For warnings, we follow the conventions:

https://github.com/microsoft/STL/blob/6b0238d7035236af0f81917262691db701e70fe3/stl/inc/yvals_core.h#L507

https://github.com/microsoft/STL/blob/6b0238d7035236af0f81917262691db701e70fe3/stl/inc/yvals_core.h#L833

Start by comparing the numbered deprecation warnings and #error messages in stl/inc/yvals_core.h with the static_assert messages in stl/inc/type_traits. Determine a numbering scheme and how uniqueness and non-reuse should be maintained. Done means the project has agreed conventions for uniformly detailed, appropriately numbered static_assert messages.