DappKit :: Adding options to the signTypedData

[Valazan]

To enhance compatibility with extension and mobile and to allow account switching when signing typed data, we should add the following optional options parameter to the signTypedData:

interface SignTypedDataOptions {
  signer?: string;
}

async signTypedData(
    _domain: ethers.TypedDataDomain,
    _types: Record<string, ethers.TypedDataField[]>,
    _value: Record<string, unknown>,
    _options?: SignTypedDataOptions
  ): Promise<string>

[victhorbi]

I would like to keep this in the RC, since next week people may already start using it.