chore: add images for X layer network and native token (#38473)

<!--
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**

This PR is to add the network image for X Layer network and for its
native token icon OKB.

[![Open in GitHub
Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/MetaMask/metamask-extension/pull/38473?quickstart=1)

## **Changelog**

CHANGELOG entry: Added the network and token icons for X Layer

## **Related issues**

Fixes:

## **Manual testing steps**

1. Open extension
2. Go to https://chainid.network/chain/196/
3. Add the network to MM by clicking on Connect
4. After accepting, It should add the network to your MetaMask
5. The icon should show correctly

## **Screenshots/Recordings**

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

### **Before**

<!-- [screenshots/recordings] -->

### **After**

<!-- [screenshots/recordings] -->

## **Pre-merge author checklist**

- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask
Extension Coding
Standards](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I’ve included tests if applicable
- [x] I’ve documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I’ve applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-extension/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.


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Adds X Layer (chainId 0xc4) with display name, OKB ticker, and
network/token icons, wiring it into all relevant maps.
> 
> - **Networks/Constants**:
>   - Add `CHAIN_IDS.X_LAYER` (`0xc4`) and `X_LAYER_DISPLAY_NAME`.
>   - Add currency symbol `CURRENCY_SYMBOLS.X_LAYER = 'OKB'`.
> - Add image URLs: `X_LAYER_IMAGE_URL`,
`X_LAYER_NATIVE_TOKEN_IMAGE_URL`.
> - **Mappings**:
>   - Map `X_LAYER` in `NETWORK_TO_NAME_MAP`.
> - Add to `CHAIN_ID_TO_CURRENCY_SYMBOL_MAP` and
`CHAIN_ID_TO_CURRENCY_SYMBOL_MAP_NETWORK_COLLISION` (where applicable).
> - Add to `CHAIN_ID_TO_NETWORK_IMAGE_URL_MAP` and
`CHAIN_ID_TOKEN_IMAGE_MAP`.
> - **Assets**:
>   - Add `app/images/x-layer.svg` and `app/images/x-layer-native.svg`.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
af2899e. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: Julink-eth