L1 live sync message validation (pre Euclid V2)

[frisitano]

I think we might be missing a couple of checks in this function:
https://github.com/scroll-tech/go-ethereum/blob/develop/core/block_validator.go#L104-L109

• Post Euclid V2: check indexes are continuous, at the start of the block and start at the last seen L1 message index.
• Pre Euclid V2: queue index can't decrease, check skipped L1 messages are in DB.

Originally posted by @greged93 in #185 (comment)