[libcxx] [test] Fix the put_double, put_long_double tests for clang-cl

These tests are hit hard by a bug that is fixed in a newer version
of UCRT. Add a test for the specific bug, and XFAIL the tests if
that bug is present (as it is in CI).

Split out hex formatting of floats to separate test files, that
are excluded with `XFAIL: msvc`. (Based on reading the C standard for
printf formatting, it seems like this isn't necessarily a proper bug
in printf, but just a case of differing optional behaviour.)

Differential Revision: https://reviews.llvm.org/D120022