load Pkg when hitting Pkg repl history

[IanButterworth]

Previously, since Pkg was moved out of the sysimage, Pkg entries in history would be skipped until Pkg was loaded.

[KristofferC]

I've been somewhat annoyed about this too but:

• It feels a bit "heavy-handed" to load all of Pkg when scrolling through history.
• It doesn't help with reverse search.

So maybe this is a good idea but it is perhaps worth pondering over it for a while if something else could be done.

[IanButterworth]

What about this one @KristofferC @Keno

Maybe we just load like this in 1.11 to avoid regression and then try to make a lighter weight history that doesn't load Pkg until the command is executed, or something?

[JeffBezanson]

Idea from @vtjnash: make all history entries always visible, but if one is from a mode that's not available use a fallback prompt mode where the text is grayed out and gives a "Pkg not loaded" error if you try to run it. Maybe also make the prompt text un-editable.

[IanButterworth]

We could pair that with the same dummy pkg prompt from #54594

[IanButterworth]

#54674 now allows scrolling through the dummy Pkg prompt if Pkg isn't loaded, then loads Pkg and executes on return.