Implement Explosion exposure for entities

[Poswn]

Issue description

• Expected result: Damage to be reduced from explosion when hiding behind blocks from tnt (probably the same for other explosions like creepers etc)
• Actual result: Take full damage of explosion through blocks (used tnt)

Steps to reproduce the issue

1. Place tnt and ignite
2. Stand behind blocks that cover you from the tnt and wait for explosion

OS and versions

• PocketMine-MP: PocketMine-MP 3.15.3 for Minecraft: Bedrock Edition v1.16.20 (protocol version 408)
• PHP: 7.3
• Server OS: Windows 10
• Game version: Win10

Plugins

Plugins (0):

• If you remove all plugins, does the issue still occur? Yes