RegExp.Result.t is unsafely typed for optional capture groups

[illusionalsagacity]

see https://forum.rescript-lang.org/t/regexp-result-t-inconsistency/5326

https://github.com/rescript-association/rescript-core/blob/0b4bd00f518430f41bdfc8703b48191b458b4ded/src/Core__RegExp.res#L4

Js.String2.match_ here is typed as returning option<array<option<t>>>