Add to/fromJSON methods to State and Accounts

This is needed since all storage in manifest v3 is key-value-pair-based
and session storage of most data is actually serialized into an
encrypted string.

libs/common/src/models/domain/encryption-pair.spec.ts

@@ -0,0 +1,44 @@
+import { Utils } from "@bitwarden/common/misc/utils";
+
+import { EncryptionPair } from "./account";
+
+describe("EncryptionPair", () => {
+  describe("toJSON", () => {
+    it("should populate decryptedSerialized for buffer arrays", () => {
+      const pair = new EncryptionPair<string, ArrayBuffer>();
+      pair.decrypted = Utils.fromByteStringToArray("hello").buffer;
+      const json = pair.toJSON();
+      expect(json.decryptedSerialized).toEqual("hello");
+    });
+
+    it("should serialize encrypted and decrypted", () => {
+      const pair = new EncryptionPair<string, string>();
+      pair.encrypted = "hello";
+      pair.decrypted = "world";
+      const json = pair.toJSON();
+      expect(json.encrypted).toEqual("hello");
+      expect(json.decrypted).toEqual("world");
+    });
+  });
+
+  describe("fromJSON", () => {
+    it("should deserialize encrypted and decrypted", () => {
+      const pair = EncryptionPair.fromJSON({
+        encrypted: "hello",
+        decrypted: "world",
+        decryptedSerialized: null,
+      });
+      expect(pair.encrypted).toEqual("hello");
+      expect(pair.decrypted).toEqual("world");
+    });
+
+    it("should deserialize decryptedSerialized for buffer arrays", () => {
+      const pair = EncryptionPair.fromJSON<string, ArrayBuffer>({
+        encrypted: "encrypted",
+        decrypted: null,
+        decryptedSerialized: "hello",
+      });
+      expect(pair.decrypted).toEqual(Utils.fromByteStringToArray("hello").buffer);
+    });
+  });
+});