Loosen up reference matching when completing lists

[radeksimko]

Context

References to lists can (and often are) addressed using indexes. One common example is creating AWS subnets for each AZ:

data "aws_availability_zones" "all" {}

resource "aws_subnet" "public" {
  count             = 3
  availability_zone = data.aws_availability_zones.all.names[count.index]
}

In which case we do not complete data.aws_availability_zones.all.names (list of strings) due to availability_zone attribute having string constraint. Such strict constraint matching is unhelpful to the user.

Proposal

Loosen up matching of references, such that list of TYPE is considered match for constraint of TYPE.