[APFloat] Prevent construction of APFloat with Semantics and FP value

Constructor invocations such as `APFloat(APFloat::IEEEdouble(), 0.0)`
may seem like they accept a FP (floating point) value, but the overload
they reach is actually the `integerPart` one, not a `float` or `double`
overload (which only exists when `fltSemantics` isn't passed).

This may lead to possible loss of data, by the conversion from `float`
or `double` to `integerPart`.

To prevent future mistakes, a new constructor overload, which accepts
any FP value and marked with `delete`, to prevent its usage.

Fixes PR34095.

Differential Revision: https://reviews.llvm.org/D70425