bug#31052: 26.0.91; Improve documentation of inline-letevals

[Gemini Lasswell <gazally@runbox.com>]

Eli Zaretskii writes:

>   When an element of @var{bindings} is just a symbol @var{var}, the
>   result of evaluating @var{var} is re-bound to @var{var}.
>
> Is this what caused you to say it "does a completely different thing
> to symbols in the binding list"?  Or did I misunderstand?
>

What caused me to say it does a completely different thing is that,
for example, if VAR is bound to 3 in an outside scope, inside:

(let (var) ...)

it will be bound to nil.  But inside

(inline-letevals (var) ...)

it will be bound to 3.  And if VAR is unbound in the outside scope,
let will bind it to nil and inline-letevals will signal an error.

It's occurred to me while writing this that

(inline-letevals (var) ...)

behaves much like

(let ((var (eval var))) ...)

although I'm not sure how to turn that into a concise explanation for
the documentation.