PhysicalProperties fail to deserialize in non-human-readable format

[DervexDev]

Currently, it's impossible to deserialize PhysicalProperties in a non-human-readable format such as MessagePack. I encounter this problem when deserializing rbx_dom_lua encoded values. As a temporary fix, I replaced:

return {
	density = roblox.Density,
	friction = roblox.Friction,
	elasticity = roblox.Elasticity,
	frictionWeight = roblox.FrictionWeight,
	elasticityWeight = roblox.ElasticityWeight,
}

with:

return {
	Custom = {
		density = roblox.Density,
		friction = roblox.Friction,
		elasticity = roblox.Elasticity,
		frictionWeight = roblox.FrictionWeight,
		elasticityWeight = roblox.ElasticityWeight,
	},
}

in rbx_dom_lua/src/EncodedValue.lua and it works just fine. However, the problem, is that it breaks deserialization of human-readable formats like JSON.

To fix this issue we should modify TaggedPhysicalProperties in rbx_types/src/physical_properties.rs. Unfortunately, I don't have time to investigate so I'm just leaving this as a tracking issue.