feat: Allow global yarnrc in XDG Base Directory compliant location

[j-px]

What's the problem this PR addresses?

Implements #3245, allowing .yarnrc.yml to be at $XDG_CONFIG_HOME/yarn/.yarnrc.yml (~/.config/yarn/.yarnrc.yml), but also still at ~/.yarnrc.yml. Both at the same time isn't allowed though, then only ~/.yarnrc.yml gets used/parsed.

How did you fix it?

Changed the home rc file finder in yarnpkg-core's Configuration.ts to find an XDG Base Directory rc file if ~/.yarnrc.yml doesn't exist.

Checklist

• I have read the Contributing Guide.

• I have set the packages that need to be released for my changes to be effective.

• I will check that all automated PR checks pass before the PR gets reviewed.

[arcanis]

My original concerns still stand:

Conceptually I know XDG is a good idea, but having a single consistent location for all global configuration makes debugging/support quite easier when all we have to say it's "check ~/.yarnrc.yml". I personally don't think XDG is worth losing that...

[j-px]

Maybe you could instead link a .yarnrc.yml docs page which mentions where the global one can be.

[Tatsh]

My original concerns still stand:

Conceptually I know XDG is a good idea, but having a single consistent location for all global configuration makes debugging/support quite easier when all we have to say it's "check ~/.yarnrc.yml". I personally don't think XDG is worth losing that...

This PR still lets ~/.yarnrc.yml exist and users by default will have the file at that location. If someone chooses to use XDG path instead it would be their conscious decision and they ought to remember. So you could say 'check ~/.yarnrc.yml or equivalent'.