Support `T[x,y,z]` patterns for arrays

[nystrom]

This is supported:

xs = [1,2,3]
@match xs begin
    [x,y,z] => ...
    ...
end

but not this:

xs = [1,2,3]
@match xs begin
    Int[x,y,z] => ...
    ...
end

[gafter]

@nystrom Is this just an idea, or do you have a use case where this would be helpful to you?

[nystrom]

Not really a use case, but I want to avoid bare arrays in my code since they lead to problems with type inference. This is not a problem in patterns, but would make the pattern syntax match the expression syntax.