This previously lacked tests altogether. This new test verifies the
"happy path", ensuring that both literal and computed values pass through
correctly into the VariableValues map.
Passing a literal map to a module looks like this in HCL:
module "foo" {
source = "./foo"
somemap {
somekey = "somevalue"
}
}
The HCL parser always wraps an extra list around the map, so we need to
remove that extra list wrapper when the parameter is indeed of type "map".
Fixes#7140