`Clients.matchAll()` should exclude the current environment

[wanderview]

With #1036 and #955 we create the possibility to use Clients.matchAll() in a way that would match the currently executing environment. This would probably be surprising to callers. I think we should exclude the "self" environment automatically. If developers end up wanting it for some reason we could add a includeSelf:true option in the future.

[jungkees]

That makes sense to me.

[wanderview]

Note, I'm fixing this in #1074.

[jakearchibald]

I pondered about clients.selfId in #1077 (comment), which might be a possibility.

[yoshisatoyanagisawa]

Bug Triage: leave this for tracking, but current spec does not have the issue mentioned here. #1036 and #955 may bring the issue in the future, though.