Bad handling of `TestFailureException` when translating unexpected
exceptions inside assertion macros led to the unexpected exceptions
handling erroring out through throwing the same exception again.

This was then backstopped by the machinery for handling uncaught
exceptions from assertions, which is normally used by the
`CATCH_CONFIG_FAST_COMPILE` machinery, where we assume that it can
only be invoked because the assertion macros are not configured to
catch assertions.

Closes #1292

In case the warning -Werror=conversion is active with GCC, the warnings
about "conversion from A to B may change value" lead to a compilation
error. This explicitly convert the values to address these warnings.

Most of these will not matter in practice due to C++14 imposing
significant limitations on what else we can make constexpr, and we cannot
have references outliving the constexpr context either way.

Technically we should be able to remove moveability as well, but
then we would need a larger surgery. This already improves the
compile times and binary sizes by a surprising amount.

Our implementation should be slightly faster, and has the
advantage of being consistent between platforms. This does not
have immediate user impact, because we currently use random_device
to generate random seed for resampling, but if we decide to change
this in the future, it is one less place to fix.

Co-authored-by: Sven Johannsen <s.johannsen@bretgeld-engineering.de>