(mostly) NFC: make Base dogfood its own APIs more sometimes (#61713)
`Base` is, of course, allowed to depend on its own internals. but that
doesn't mean it always should. when possible I think we should prefer to
use public alternatives vs private when equivalents of each are
available.
includes an unintentional bugfix to `help?>` of any intrinsic, which on
master leads you to the docstring for `Core.IntrinsicFunction` itself.
candidates generated by claude, which I then audited