Players suffocate inside of slime blocks

Relates to MC-50648, MC-139394 and MC-311834.

Ever since their introduction, despite being visually translucent, slime blocks have dealt suffocation damage to entities. This is inconsistent with every other translucent block in the game besides ice (MC-50648).

Expected result: slime blocks, like honey blocks and stained glass, would not suffocate players.

Actual results: they do.