Add getAssetMetadata action to MultichainAssetsController (#5430)

## Explanation

This adds an action to the `MultichainAssetsController` called
`getAssetMetada` which allows to get a specific asset Metadata.

This allows us to get a specific metadata without having to pull the
entire controller state.

## References

* Related to MetaMask/snaps#3166

## Changelog

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### `@metamask/assets-controller`

- **ADDED**: Add `getAssetMetadata` action to
`MultichainAssetsController`.

## Checklist

- [ ] I've updated the test suite for new or updated code as appropriate
- [ ] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [ ] I've highlighted breaking changes using the "BREAKING" category
above as appropriate
- [ ] I've prepared draft pull requests for clients and consumer
packages to resolve any breaking changes

Author: GuillaumeRx

packages/assets-controllers/src/MultichainAssetsController/MultichainAssetsController.test.ts

@@ -773,4 +773,49 @@ describe('MultichainAssetsController', () => {
       });
     });
   });
+
+  describe('getAssetMetadata', () => {
+    it('returns the metadata for a given asset', async () => {
+      const { messenger } = setupController({
+        state: {
+          accountsAssets: {
+            [mockSolanaAccount.id]: mockHandleRequestOnAssetsLookupReturnValue,
+          },
+          assetsMetadata: mockGetMetadataReturnValue.assets,
+        } as MultichainAssetsControllerState,
+      });
+
+      const assetId = 'solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1/slip44:501';
+
+      const metadata = messenger.call(
+        'MultichainAssetsController:getAssetMetadata',
+        assetId,
+      );
+
+      expect(metadata).toStrictEqual(
+        mockGetMetadataReturnValue.assets[assetId],
+      );
+    });
+
+    it('returns undefined if the asset metadata is not found', async () => {
+      const { messenger } = setupController({
+        state: {
+          accountsAssets: {
+            [mockSolanaAccount.id]: mockHandleRequestOnAssetsLookupReturnValue,
+          },
+          assetsMetadata: mockGetMetadataReturnValue.assets,
+        } as MultichainAssetsControllerState,
+      });
+
+      const assetId =
+        'solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp/token:EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v';
+
+      const metadata = messenger.call(
+        'MultichainAssetsController:getAssetMetadata',
+        assetId,
+      );
+
+      expect(metadata).toBeUndefined();
+    });
+  });
 });

packages/assets-controllers/src/MultichainAssetsController/MultichainAssetsController.ts

@@ -69,6 +69,11 @@ export function getDefaultMultichainAssetsControllerState(): MultichainAssetsCon
   return { accountsAssets: {}, assetsMetadata: {} };
 }
 
+export type MultichainAssetsControllerGetAssetMetadataAction = {
+  type: `${typeof controllerName}:getAssetMetadata`;
+  handler: MultichainAssetsController['getAssetMetadata'];
+};
+
 /**
  * Returns the state of the {@link MultichainAssetsController}.
  */
@@ -90,7 +95,8 @@ export type MultichainAssetsControllerStateChangeEvent =
  * Actions exposed by the {@link MultichainAssetsController}.
  */
 export type MultichainAssetsControllerActions =
-  MultichainAssetsControllerGetStateAction;
+  | MultichainAssetsControllerGetStateAction
+  | MultichainAssetsControllerGetAssetMetadataAction;
 
 /**
  * Events emitted by {@link MultichainAssetsController}.
@@ -199,6 +205,8 @@ export class MultichainAssetsController extends BaseController<
       'AccountsController:accountAssetListUpdated',
       async (event) => await this.#handleAccountAssetListUpdatedEvent(event),
     );
+
+    this.#registerMessageHandlers();
   }
 
   async #handleAccountAssetListUpdatedEvent(
@@ -215,6 +223,27 @@ export class MultichainAssetsController extends BaseController<
     );
   }
 
+  /**
+   * Constructor helper for registering the controller's messaging system
+   * actions.
+   */
+  #registerMessageHandlers() {
+    this.messagingSystem.registerActionHandler(
+      'MultichainAssetsController:getAssetMetadata',
+      this.getAssetMetadata.bind(this),
+    );
+  }
+
+  /**
+   * Returns the metadata for the given asset
+   *
+   * @param asset - The asset to get metadata for
+   * @returns The metadata for the asset or undefined if not found.
+   */
+  getAssetMetadata(asset: CaipAssetType): FungibleAssetMetadata | undefined {
+    return this.state.assetsMetadata[asset];
+  }
+
   /**
    * Function to update the assets list for an account
    *