improve getproperty(Pairs) warnings (#55989)

- Only call `depwarn` if the field is `itr` or `data`; otherwise let the field error happen as normal
- Give a more specific deprecation warning.

Author: aplavin

base/deprecated.jl

@@ -432,7 +432,8 @@ const All16{T,N} = Tuple{T,T,T,T,T,T,T,T,
 
 # the plan is to eventually overload getproperty to access entries of the dict
 @noinline function getproperty(x::Pairs, s::Symbol)
-    depwarn("use values(kwargs) and keys(kwargs) instead of kwargs.data and kwargs.itr", :getproperty, force=true)
+    s == :data && depwarn("use values(kwargs) instead of kwargs.data", :getproperty, force=true)
+    s == :itr && depwarn("use keys(kwargs) instead of kwargs.itr", :getproperty, force=true)
     return getfield(x, s)
 end