More intuitive constructor names for TypedVarInfo and UntypedVarInfo

[yebai]

Current way to construct typed and untyped VarInfo:

# Untyped VarInfo 
vi = VarInfo()
model(rng, vi)
vi

# Typed VarInfo 
VarInfo(rng, model)

A more intuitive way would be

# Untyped VarInfo 
UntypedVarInfo(rng, model)


# Typed VarInfo 
TypedVarInfo(rng, model)

See, e.g.: https://github.com/TuringLang/DynamicPPL.jl/pull/861/files#diff-453c0f6cda4a57b858cf8a049aa4e0d01085433ca084c71982ff18da3684e324R38-R46

[penelopeysm]

The SimpleVarInfos need better constructors too imo.

[penelopeysm]

see also

DynamicPPL.jl/src/test_utils/varinfo.jl

Lines 17 to 69 in fb5413f

	"""
	setup_varinfos(model::Model, example_values::NamedTuple, varnames; include_threadsafe::Bool=false)
	Return a tuple of instances for different implementations of `AbstractVarInfo` with
	each `vi`, supposedly, satisfying `vi[vn] == get(example_values, vn)` for `vn` in `varnames`.
	If `include_threadsafe` is `true`, then the returned tuple will also include thread-safe versions
	of the varinfo instances.
	"""
	function setup_varinfos(
	model::Model, example_values::NamedTuple, varnames; include_threadsafe::Bool=false
	)
	# VarInfo
	vi_untyped_metadata = VarInfo(DynamicPPL.Metadata())
	vi_untyped_vnv = VarInfo(DynamicPPL.VarNamedVector())
	model(vi_untyped_metadata)
	model(vi_untyped_vnv)
	vi_typed_metadata = DynamicPPL.TypedVarInfo(vi_untyped_metadata)
	vi_typed_vnv = DynamicPPL.TypedVarInfo(vi_untyped_vnv)
	# SimpleVarInfo
	svi_typed = SimpleVarInfo(example_values)
	svi_untyped = SimpleVarInfo(OrderedDict())
	svi_vnv = SimpleVarInfo(DynamicPPL.VarNamedVector())
	# SimpleVarInfo{<:Any,<:Ref}
	svi_typed_ref = SimpleVarInfo(example_values, Ref(getlogp(svi_typed)))
	svi_untyped_ref = SimpleVarInfo(OrderedDict(), Ref(getlogp(svi_untyped)))
	svi_vnv_ref = SimpleVarInfo(DynamicPPL.VarNamedVector(), Ref(getlogp(svi_vnv)))
	lp = getlogp(vi_typed_metadata)
	varinfos = map((
	vi_untyped_metadata,
	vi_untyped_vnv,
	vi_typed_metadata,
	vi_typed_vnv,
	svi_typed,
	svi_untyped,
	svi_vnv,
	svi_typed_ref,
	svi_untyped_ref,
	svi_vnv_ref,
	)) do vi
	# Set them all to the same values.
	DynamicPPL.setlogp!!(update_values!!(vi, example_values, varnames), lp)
	end
	if include_threadsafe
	varinfos = (varinfos..., map(DynamicPPL.ThreadSafeVarInfo ∘ deepcopy, varinfos)...)
	end
	return varinfos
	end

[penelopeysm]

Closed by #879, released in 0.36 #829