[Bug]: Advanced Permissions requests fail with `Invalid input`

When serving `wallet_grantExecutionPermissions` requests, the RPC returns early with `Invalid input` error.

## Reproduction steps

- visit the Advanced Permissions development site https://github.com/MetaMask/snap-7715-permissions/tree/main/packages/site
- click "Grant Permissions"
- click "Grant" on the Permission Picker dialog

**Actual**
Error is returned.

**Expected**
Sign permission confirmation is shown.

## Root cause

This is a result of the tighter `eth_signTypedData_v4` validation in https://github.com/MetaMask/core/pull/8526 that expressly forbids extraneous properties in the `eth_signTypedData_v4` payload.

Advanced Permissions specifies `metadata` as a top level property on the payload, which is not included in the `types` being signed.

Start by tracing the wallet_grantExecutionPermissions RPC flow and its eth_signTypedData_v4 payload handling, using the Advanced Permissions development site at packages/site to reproduce the failure. Confirm that the request reaches the permission confirmation instead of returning Invalid input, while preserving the stricter validation for unrelated payloads.

Written by the indexing model from the issue text.