Additional identity methods (FuelLabs#4683)

## Description
Added some utility methods to the Identity struct

## Checklist

- [] I have linked to any relevant issues.
- [ ] I have commented my code, particularly in hard-to-understand
areas.
- [ ] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [x] I have added tests that prove my fix is effective or that my
feature works.
- [ ] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [x] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [x] I have requested a review from the relevant team or maintainers.

sway-lib-std/src/identity.sw

@@ -2,8 +2,11 @@
 //! The use of this type allows for handling interactions with contracts and addresses in a unified manner.
 library;
 
+use ::assert::assert;
 use ::address::Address;
+use ::constants::{ZERO_B256, BASE_ASSET_ID};
 use ::contract_id::ContractId;
+use ::option::Option;
 
 /// The `Identity` type: either an `Address` or a `ContractId`.
 // ANCHOR: docs_identity
@@ -21,3 +24,53 @@ impl core::ops::Eq for Identity {
         }
     }
 }
+
+impl Identity {
+    pub fn as_address(self) -> Option<Address> {
+        match self {
+            Identity::Address(address) => Option::Some(address),
+            Identity::ContractId(_) => Option::None,
+        }
+    }
+
+    pub fn as_contract_id(self) -> Option<ContractId> {
+        match self {
+            Identity::Address(_) => Option::None,
+            Identity::ContractId(contract_id) => Option::Some(contract_id),
+        }
+    }
+
+    pub fn is_address(self) -> bool {
+        match self {
+            Identity::Address(_) => true,
+            Identity::ContractId(_) => false,
+        }
+    }
+
+    pub fn is_contract_id(self) -> bool {
+        match self {
+            Identity::Address(_) => false,
+            Identity::ContractId(_) => true,
+        }
+    }
+}
+
+#[test]
+fn test_address() {
+    let address = Address::from(ZERO_B256);
+    let identity = Identity::Address(address);
+    assert(identity.is_address());
+    assert(!identity.is_contract_id());
+    assert(identity.as_address().unwrap() == address);
+    assert(identity.as_contract_id().is_none());
+}
+
+#[test]
+fn test_contract_id() {
+    let contract_id = BASE_ASSET_ID;
+    let identity = Identity::ContractId(contract_id);
+    assert(!identity.is_address());
+    assert(identity.is_contract_id());
+    assert(identity.as_contract_id().unwrap() == contract_id);
+    assert(identity.as_address().is_none());
+}