added back def of untyped_varinfo that shouldn't have been removed +

fixed call in docs

Author: torfjelde

docs/src/internals/varinfo.md

@@ -79,7 +79,7 @@ For example, with the model above we have
 
 ```@example varinfo-design
 # Type-unstable `VarInfo`
-varinfo_untyped = DynamicPPL.untyped_varinfo(demo(), SamplingContext(), DynamicPPL.Metadata())
+varinfo_untyped = DynamicPPL.untyped_varinfo(demo())
 typeof(varinfo_untyped.metadata)
 ```
 

src/varinfo.jl

@@ -177,6 +177,11 @@ function untyped_varinfo(
 )
     return untyped_varinfo(model, SamplingContext(rng, sampler, context), metadata)
 end
+function untyped_varinfo(
+    model::Model, args::Union{AbstractSampler,AbstractContext,Metadata,VarNamedVector}...
+)
+    return untyped_varinfo(Random.default_rng(), model, args...)
+end
 function untyped_varinfo(
     model::Model,
     context::AbstractContext,