chore!: Remove snap_experimentalProviderRequest

[FrederikBolding]

Remove snap_experimentalProviderRequest which was a temporary experimental way to provide the multichain API. We explicitly flagged that it may be removed at any time and don't know of any active use.

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Note

Medium Risk
Breaking API removal: any Snap relying on snap_experimentalProviderRequest or its SDK types will fail to compile or call the method. Runtime risk is otherwise low since this mainly deletes code and associated tests.

Overview
Removes the experimental snap_experimentalProviderRequest JSON-RPC method by deleting its handler implementation and test, and unregistering it from the permitted methodHandlers map.

Removes the corresponding SDK type exports (ProviderRequestParams/ProviderRequestResult) by deleting provider-request.ts and dropping it from types/methods/index.ts, and slightly adjusts Jest coverage thresholds to reflect the deletion.

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[cryptodev-2s]

Looks like this file is still being referenced

packages/snaps-rpc-methods/src/permitted/index.ts:6:49 - error TS2307: Cannot find module './experimentalProviderRequest' or its corresponding type declarations.