Cleanup damage source a bit

[Lulu13022002]

Closes #11025

[lynxplay]

Generally I like the cleanup, passing the cause like this is a lot nicer.
The thing I am a bit confused on is the withers/setters in DamageSource now.
Some are withers, e.g. perform a copy, others actually mutate the instance.
It seems semi arbitrary, presumably this is fine like this as the setters are only called on instances copied prior, however that feels pretty much like we are asking for an explosion down the line given the inconsistent behaviour here.

The two setters, critial and customBlockState, are I think not in a hot enough code path where the one extra copy of a damage source (which involves 0 deep copying anyway) would be a problem.
Are there other reasons I missed as to why you decided to make them setters?