Fix Project equality when compat entries are present

[IanButterworth]

The compat field of a Project appears to breaking equality even when the projects are identical.

julia> Pkg.Types.Compat(Pkg.Types.VersionSpec("0.1"), "0.1") == Pkg.Types.Compat(Pkg.Types.VersionSpec("0.1"), "0.1")
false

This was observed in JuliaRegistries/General#47659 (comment) where an unchanged Project was being re-written to disk, without any actual changes to the file even though this check should prevent that

I'm adding the tests first to prove the problem exists first.

Also, @staticfloat the pkgserver tests are failing with

┌ Warning: could not download https://pkg.julialang.org/registries
│   exception = HTTP/1.1 502 Bad Gateway while requesting https://pkg.julialang.org/registries
└ @ Pkg.Registry ~/Documents/GitHub/Pkg.jl/src/Registry/Registry.jl:66

[staticfloat]

PkgServer breakage has been fixed.

[fredrikekre]

Is this equality check used for something other than #2202 ? That PR didn't implement it so I guess so? Possibly another internal function should be used instead of overloading == and hash then.

[IanButterworth]

Sorry, I don't follow. I may be being slow though..

This PR specifically fixes a bug in the behavior introduced in #2202 where it will alway re-write a Project when compat fields are present. And because the equality check #2202 uses is just ==(::Project, ::Project) I don't see how fixing this could be anything other than defining == and hash for Compat?

[fredrikekre]

I just meant that probably == as used in #2202 could be switched to use something like have_same_toml_representation(p1, p2)::Bool function instead. But since #2202 didn't add the equality check maybe it is used for something else?

[KristofferC]

I don't think this applies to 1.6.