deprecate boolean evaluation of floating point and character types

[Nick Treleaven]

On Tuesday, 30 April 2024 at 17:01:42 UTC, Basile B. wrote:
> Generally there is a strong correlation between default 
> initialization and boolean evaluation to `false`.

But the meaning of boolean evaluation of a number is to check if 
it is non-zero. That is well established from C.

> instead of an assertion failure what we should get is rather a 
> message such as
>
>    error, cannot evaluate `f64` to a `bool`

Why break D code that was written with the non-zero test 
expectation? Why make porting from C harder yet still allow 
non-zero tests for integers? Wouldn't that be more confusing?