Add an updated EIP-1271 function to the WebAuthn signer

[mmv08]

This PR:

• Adds an updated EIP-1271 validation method to the WebAuthnSigner contract for futureproofing
• I created an abstract contract with both magic values, similar to how it's done in the Safe Account contract. We cannot reuse the Safe's contract because it only includes one value (either the legacy or the new one)
• I had to adjust the return values of signature-validating functions slightly. For the generic checkSignatures function, I changed it to a boolean, similar to how it's done in the underlying FCL's validation function

[coveralls]

Pull Request Test Coverage Report for Build 7530149666

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-2.4%) to 82.738%

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Totals
Change from base Build 7504336477:	-2.4%
Covered Lines:	101
Relevant Lines:	110

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💛 - Coveralls