feat(types): add Math.sumPrecise and Intl.Locale.prototype.variants (#34287)
Both `Math.sumPrecise` and `Intl.Locale.prototype.variants` are
available at runtime via V8, but our bundled TypeScript libs (currently on 6.0)
don't yet declare them, so `deno check` errors with TS2339 whenever user
code references either API. This adds the missing typings to
`lib.deno.shared_globals.d.ts` so both stable and worker contexts pick
them up. `variants` is typed as `string` to match the spec, which
returns the variant subtags joined by `-` (e.g. `"1996-fonipa"`).