[v2][e2e] Signature redesign - Create malformed signature tests

ref: https://github.com/MetaMask/metamask-extension/issues/23552#issuecomment-2017496179

Create e2e tests:
- [ ] Malformed signatures

Not ready:
- Needs more discussion
- Need to discuss and implement malformed signature handling

Start with the discussion linked from issue 23552, especially the referenced comment, and clarify the expected malformed-signature handling before locating the end-to-end test entry points. Done means the handling decision is implemented and malformed signature cases are covered by passing e2e tests.

Written by the indexing model from the issue text.