Brian Goff 1ad87c6ba6 Update go-cty to pull in more stdlib funcs.
I needed "split" specifically so I can do something like:

```hcl
variable PLATFORMS {
  default = "linux/amd64"
}

target foo {
  platforms = split(",", "${PLATFORMS}")
  # other stuff
}
```

Where the existing "csvdecode" does not work for this because it parses
the string into a list of objects instead of a list of strings.

I went ahead and just added all the available new functions.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>
..
convert Update go-cty to pull in more stdlib funcs.
function Update go-cty to pull in more stdlib funcs.
gocty Modify parsing functions and config structs to accept hcl changes
json Modify parsing functions and config structs to accept hcl changes
set Upgrade hcl to v2
capsule.go Upgrade hcl to v2
capsule_ops.go Upgrade hcl to v2
collection.go Upgrade hcl to v2
doc.go Upgrade hcl to v2
element_iterator.go Upgrade hcl to v2
error.go Upgrade hcl to v2
gob.go Upgrade hcl to v2
helper.go Upgrade hcl to v2
json.go Upgrade hcl to v2
list_type.go Upgrade hcl to v2
map_type.go Upgrade hcl to v2
marks.go Update go-cty to pull in more stdlib funcs.
null.go Upgrade hcl to v2
object_type.go Upgrade hcl to v2
path.go Update go-cty to pull in more stdlib funcs.
path_set.go Upgrade hcl to v2
primitive_type.go Upgrade hcl to v2
set_helper.go Upgrade hcl to v2
set_internals.go Upgrade hcl to v2
set_type.go Upgrade hcl to v2
tuple_type.go Upgrade hcl to v2
type.go Upgrade hcl to v2
type_conform.go Upgrade hcl to v2
types_to_register.go Upgrade hcl to v2
unknown.go Upgrade hcl to v2
unknown_as_null.go Upgrade hcl to v2
value.go Upgrade hcl to v2
value_init.go Upgrade hcl to v2
value_ops.go Upgrade hcl to v2
walk.go Upgrade hcl to v2