[m-rev.] for post-commit review: improve diagnostics for bad number literals

[Julien Fischer]

On Mon, 19 Jun 2023, Zoltan Somogyi wrote:

> For review by anyone. I would like feedback on two things
> in particular: the text of the error messages, and whether
> we should continue to generate an error for an underscore
> before the exponent in a float. I see no reason for the ban,
> and any motivation rooted in Prolog compatbility is long
> in the past.

Prolog compatibility was never a motivation for where underscores are
allowed in numeric literals. At the time I added support for that, I
just looked at what a bunch of other programming languages that allow
underscores do and did what was most common. I see no issue with
allowing underscores before exponents.

The diff is fine.

Julien.