Make PrecompileTools into a stdlib

[timholy]

This makes PrecompileTools an upgradable stdlib.
While it will still live in its own repository, this allows
it to be used by other stdlibs to lower their TTFX
when they migrate out.

[timholy]

After a slack discussion with @KristofferC, we concluded that because we'd also need to make Preferences an upgradable stdlib, it might be better to vendor the ~60LOC needed from PrecompileTools.

[vchuravy]

I think we only didn't make preferences as stdlib, because at the time we hadn't figured out how to make them upgradeable.

@staticfloat and I want to eventually use Preferences for behaviour in Base (but not include Preferences in the sysimg)

[timholy]

I'm happy to reopen this if we get to a point where we want it.

[vchuravy]

I now want this :)

[timholy]

Back from the dead! But we'll need Preferences before we can merge this, I think.

[KristofferC]

I now want this :)

Why?

But we'll need Preferences before we can merge this, I think.

:(

[vchuravy]

I originally thought I would need it for #51350, but I was mistaken.

I can see a use for this when we have a lot of upgradeable stdlibs that don't want to maintain explicit precompile statement lists.

(We could also vendor a Preference free version, but I don't feel to bad about making Preferences an upgradeable stdlib.)

[mkitti]

Could we move some code from PrecompileTools.jl into Base or Core?

In particular, the ccalls really should be wrapped into a Julia function.

ccall(:jl_generating_output, Cint, ())
ccall(:jl_debug_method_invalidation, Any, (Cint,), 1)