Fixes https://github.com/payloadcms/payload/issues/11901
Previously, when `ValidationError` `errors.path` was referring to a
field with `label` defined as a function, the error message was
generated with `[object Object]`. Now, we call that function instead.
Since the `i18n` argument is required for `StaticLabel`, this PR
introduces so you can pass a partial `req` to `ValidationError` from
which we thread `req.i18n` to the label args.
dc793d1d14