ECMA-262 implies that `MIN_VALUE` should be a denormalized value if
denormal arithmetic is supported. This is the case on x86-64 and AArch64
using standard GCC/Clang compilation settings.
test262 checks whether `Number.MIN_VALUE / 2.0` is equal to 0, which
only holds if `MIN_VALUE` is the smallest denormalized value.
This commit renames the existing `NumericLimits<FloatingPoint>::min()`
to `min_normal()` and adds a `min_denormal()` method to force users to
explicitly think about which one is appropriate for their use case. We
shouldn't follow the STL's confusingly designed interface in this
regard.