Add knockback to the player when using a shield

I think a little bit of knockback should be added when blocking mobs with a shield, a medium  amount for explosions, and make shields against the dragon block that damage, using 10-20% durability, but still have 65% of the knockback.

On bugtracker, many have reported that when a slime/maga cube/dragon is attacking, they spam attack and their knockback is supposed to move you out of the range after 1-2 hits, But shielding makes you not get knockback and your shield gets teared through in less then a second. My proposed solution is to make slimes/magma cubes bounce off the shield, doing 5-10%durability, so they can't destroy your shield as fast. In fortresses, a shield is the most important thing, for fighting wither skeletons, blocking blazes, and it seems unfair how one mob can just take the shield away instantly, leaving you without protection. These changes would make blocking with a shield more fair and fix dragon/slime/magma cubes destroying shields almost instantly.