Bug: [EMN] Slayer's Cleaver blocking requirement

To track the remaining discrepancies as noticed in #10327

[[Slayer's Cleaver]]

1. Combat can't move forward if the blocking requirement interferes with a blocking restriction. To reproduce, equip the cleaver to a creature with menace, and attack into a single Eldrazi with no other creatures.
2. The blocking requirement forces all Eldrazi to block if able, but only a single Eldrazi is required to block.

Not sure whether these can be fixed without some adjustments to the combat engine.

Reproduce the issue with Slayer's Cleaver on a creature with menace attacking a single Eldrazi, then trace the combat engine's blocking requirement and restriction handling. The fix is complete when combat can proceed in that scenario and the requirement makes only one Eldrazi block when only one blocker is required.

Written by the indexing model from the issue text.