Coalesce inline and normal alias headers

Unifies `As` annotations and `Alias` defs to use a common struct for
defining alias header information, i.e. the name and type variables of
the alias.

compiler/fmt/src/annotation.rs

@@ -254,7 +254,8 @@ impl<'a> Formattable for TypeAnnotation<'a> {
                 buf.push_str(name.value);
                 for var in *vars {
                     buf.spaces(1);
-                    buf.push_str(var.value);
+                    var.value
+                        .format_with_options(buf, Parens::NotNeeded, Newlines::No, indent);
                 }
             }