Refactoring: split ElementType away from the types used as property type

These are two different concept, and it is confusing to keep them in the
same enum

We want to support component without any base element, and Void is
already used for global component, so do this refactoring before

internal/compiler/llr/expression.rs

@@ -182,9 +182,6 @@ impl Expression {
     pub fn default_value_for_type(ty: &Type) -> Option<Self> {
         Some(match ty {
             Type::Invalid
-            | Type::Component(_)
-            | Type::Builtin(_)
-            | Type::Native(_)
             | Type::Callback { .. }
             | Type::Function { .. }
             | Type::Void