fix UB in value::emplace_ functions

With enough optimisations emplace functions accessed an object after its
lifetime has ended, due to order of evaluation. The fix is to make the
correct order correct.

release notes for 1.91.0

work around clang bug in visit

fix typo

fix typo

documentation fixes

remove custom alignas check

The check was added because of older GCC versions which are no longer
supported

remove custom alignas check

The check was added because of older GCC versions which are no longer
supported

remove unnecessary branch in string serialization

remove unnecessary branch in string serialization