change parsing of `~` from macro to operator

[StefanKarpinski]

From #19598:

• change parsing of ~ in Base from macro to plain infix operator (fix #20406, parse infix ~ as a normal operator #20420)

• change the one user of this as a macro – i.e. StatsModels (WIP: Replace infix ~ for formulas with a model macro JuliaStats/StatsModels.jl#9)

• update DataFrames to depend on the new version of StatsModels (issue/PR link?)

[JeffBezanson]

Currently this has n-ary parsing; x ~ y ~ z is parsed as a single 3-argument call. Do we want to keep that?

[ararslan]

Regarding updating DataFrames, the situation is a little complex, but we're getting there. Ref JuliaData/DataFrames.jl#1154 (comment)

[ararslan]

@JeffBezanson I've never seen that used in the wild (and indeed I didn't even know about it) so I'd guess that if that behavior were removed with the parsing change, few people if anyone would notice. So if it's simpler to take it out then I'd say go for it.

[StefanKarpinski]

Good point: try parsing as binary and see if anyone screams 😬

[GunnarFarneback]

For what it's worth I have made use of the n-ary parsing, but it's moot when the macro parsing goes away.