chore(runway): cherry-pick fix: cp-7.49.0 eth_signTypedData_v4 on Multichain API (#16318)

<!--
Please submit this PR as a draft initially.
Do not mark it as "Ready for review" until the template has been
completely filled out, and PR status checks have passed at least once.
-->

## **Description**

The following
[PR](#16054)
accidentally undid the changes to the `eth_signTypedData_v4` RPC method
handler previously brought in by [this
PR](#15837).

So we want to make sure to bring in these changes again.

<!--
Write a short description of the changes included in this pull request,
also include relevant motivation and context. Have in mind the following
questions:
1. What is the reason for the change?
2. What is the improvement/solution?
-->

## **Related issues**

Fixes: MetaMask/MetaMask-planning#4951

## **Manual testing steps**

1. Go to [Multichain Test
Dapp](https://metamask.github.io/test-dapp-multichain/latest/) via in
app browser
2. Connect to an EVM Chain
3. Make sure per dapp selected network is set to the chain in which the
`eth_signTypedData_v4` request will be sent
4. In the scope for the selected chain, select the
`eth_signTypedData_v4` method and press "Invoke Method" button

## **Screenshots/Recordings**

<!-- If applicable, add screenshots and/or recordings to visualize the
before and after of your change. -->

### **Before**


https://github.com/user-attachments/assets/a7e9c607-c879-409d-a8ba-eedd4d0f52e5

### **After**


https://github.com/user-attachments/assets/3533951c-ee00-4414-99e7-efed3d21b2ee

## **Pre-merge author checklist**

- [ ] I’ve followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
Coding
Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [ ] I've completed the PR template to the best of my ability
- [ ] I’ve included tests if applicable
- [ ] I’ve documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [ ] I’ve applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

Author: ffmcgee725

app/core/RPCMethods/RPCMethodMiddleware.ts

@@ -818,10 +818,11 @@ export const getRpcMethodMiddleware = ({
         });
       },
 
-      // TODO: Fix for Multichain API call via wallet_invokeMethod. Currently this RPC method is broken for Multichain.
-      // ticket with details regarding the issue here: https://github.com/MetaMask/MetaMask-planning/issues/4951
       eth_signTypedData_v4: async () => {
-        const data = JSON.parse(req.params[1]);
+        const data =
+          typeof req.params[1] === 'string'
+            ? JSON.parse(req.params[1])
+            : req.params[1];
         const chainId = data.domain.chainId;
 
         trace(