Excise FileWatching by moving pidfile to Base

[vchuravy]

I am slowly redefining what it means to be a stdlib.
Previously we have used stdlibs as a way to organize code,
outside the monolith that is base/. With a move towards
stdlibs using pkgimages as their caching mechanism and them
becoming upgradeable, we have to redefine the relationship
between Base and stdlibs.

In my opinion Base should not have a direct dependency on
functionality in standard libraries. If we need something to be used by Base,
we must include the minimal set of functionality.
Functions in Base should either be universally useful,
or require some sort of compiler/runtime support.

Since we are not breaking functionality we must allow for
auto-loading/delayed loading of packages, but that mechanism,
must allow for the loading to fail.

Pidfile support was introduced in #44367, but it only uses
a watch_file from FileWatching.jl.

Here I moved pidfile.jl to base, removing the usage of FileWatching.
I decided against delayed initialization, since there would be a
rather annoying recusrion potential, and we don't want users to
disallow @stdlib and then suddenly have cache races again.

[IanButterworth]

The strategy sounds reasonable to me but I defer to @vtjnash about the removal of use of watch_file in Pidfile.

[IanButterworth]

bump @vtjnash

[LilithHafner]

Triage didn't haven anyone who understood these code paths deeply but it seemed like a good idea from the outside.

• Where does this functionality really belong?
• Is it worth splitting the library (e.g. do we want pidfiles and file watching to be in the same place)

[LilithHafner]

I'm a big fan of excision and want to make sure that this gets any support it needs, but I'm not sure how discussing this on triage would help. Feel free to re-add the label with a note about what specifically you would like discussed.

[IanButterworth]

Any particular reason for the close? (didn't mean to sound negative. Just interested)

[vchuravy]

Mostly me just un-licking the cookie and acknowledging that I won't be able to work on this until I graduated

[KristofferC]

I won't be able to work on this until I graduated

@vchuravy you graduated now, right? Reopen? 😆 😆