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!

@densh 's comments on the ticket are longer than the fix and the test.

Review by @densh

That's quite surprising. It turns out that quasiquotes have the same issue here:
```
scala> q"${1} + ${1.0}"
res1: reflect.runtime.universe.Tree = 1.0.$plus(1.0)
```
Please add this bound to quasiquote interpolator definition too https://github.com/scala/scala/blob/2.12.x/src/reflect/scala/reflect/api/Quasiquotes.scala#L16