Add entity placer type and default

[Nathan93705]

No description provided.

[Xterionix]

I believe this also accepts an object for the tags so this isn't right

[DaanV2]

Seem they have documentation on it:

https://learn.microsoft.com/en-us/minecraft/creator/reference/content/itemreference/examples/itemcomponents/minecraft_entity_placer?view=minecraft-bedrock-stable#dispense-on-properties

so we can update it :)

[Xterionix]

I'm pretty sure there's a general block descriptor schema somewhere on the repo. It should just link back to that