SI-8512 Infer a type for f"$args"

The f-interpolator gets a type param that better be Any to avoid
unfortunate widenings.

Hey, it worked!

Unfortunately, when `Any` is inferred, `-Xlint:infer-any` takes notice.

This is probably a greater problem for the f-interpolator than for
quasiquotes, which are a more specialized tool.
SI-8512 Infer Any for the q

Avoid the widening bug for q.  This resolution also suffers
from the inference of Any, which can trigger a warning and
an anxiety attack.  But that's still better than doing the
wrong thing.

Right?
Merge pull request #3909 from som-snytt/issue/8512

SI-8512 Infer a type for f"$args"