bug#65459: completing-read INITIAL-VALUE unaware of COLLECTION and REQUIRE-MATCH

[Stefan Monnier]

> Additionally, let's have minibuffer prefilling as part of the design
> without any discouragement or encouragement regarding its use.
> I like it, others don't like it.

This last sentence is key: it should not be a choice of the caller of the
function, but should depend on the configuration of the UI instead.

Using DEFault makes this customization possible.  Using INITIAL-INPUT
does not.


        Stefan