[WIP] Incorrect behaviours of CORE:: and CLIENT:: pseudo-packages

[vrurg]

The Problem

When used in GLOBAL package CLIENT:: fails with GLOBAL can have no client package error. This is incorrect because code defined in GLOBAL can be passed to a routine in another module:

module Foo {
    sub foo (&c) is export {
        c
    }
}
import Foo;
sub bar(Str:D $s) {
    say CLIENT::.WHAT
}
foo(&bar)

This ticket is an anchor for work in progress.

[vrurg]

Closed via #3105 and Raku/roast#564