feat: add originMetadata to submitRequest

[FrederikBolding]

Description

Add an optional originMetadata field to submitRequest, which will only be passed down in v2 keyrings or in v1 keyrings that are using at least platform version 12. This field can be used when using transports where the origin itself isn't verifiable.

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Note

Medium Risk
Touches signing request routing and platform-gated payload shaping; backward compatibility is explicit but wrong version checks could break older Snaps or omit metadata for new ones.

Overview
Adds optional originMetadata (transport, selfReportedOrigin) on KeyringRequest and threads it through submitRequest so Snaps can reason about callers when the origin string alone is not trustworthy (e.g. WalletConnect).

SnapKeyring / SnapKeyringV1 choose the RPC shape from Snap platform version: ≥12.0.0 sends full requests (including metadata when provided); 7.0.0–11.x uses new toKeyringRequestWithoutOriginMetadata / submitRequestWithoutOriginMetadata; older platforms still strip origin. toKeyringRequestWithoutOrigin now also drops originMetadata. EthKeyringV1Adapter always passes originMetadata: null on internal submits.

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