Using gohcl, escape characters required for HCL parsing remain in the decoded string field

Given the following string in HCL2 the \\ required to parse \/:

`"^whatever\\/.*$"`

When decoding with gohcl into a struct the resulting string within the struct still contains the extra \

```
Acl: (*model.Acl)(0xc4201b2080)({
Resources: ([]*model.Resource) (len=5 cap=5) {
(*model.Resource)(0xc420157d70)({
Pattern: (string) (len=13) "^whatever\\/.*$",
Permissions: ([]*model.Permission) (len=2 cap=2) {
(*model.Permission)(0xc4201b40f0)({
Authority: (string) (len=15) "role:nacho_rw",
Actions: ([]string) (len=2 cap=2) {
(string) (len=4) "pull",
(string) (len=4) "push"
}
}),
```
I would expect that the when decoding the string escape is removed?

Start at the gohcl decoding path and reproduce the HCL2 example containing an escaped slash. Compare the decoded struct field with the expected unescaped string, then add coverage for this case and confirm the resulting value no longer contains the parsing escape.

Written by the indexing model from the issue text.