Minor refactor

codegen/ui_tests/export_fn_raw_noreturn.stderr

@@ -1,4 +1,4 @@
-error: return_raw functions must return Result<T, Box<EvalAltResult>>
+error: functions marked with 'return_raw' must return Result<Dynamic, Box<EvalAltResult>>
   --> $DIR/export_fn_raw_noreturn.rs:10:5
    |
 10 | pub fn test_fn(input: &mut Point) {

codegen/ui_tests/export_mod_raw_noreturn.stderr

@@ -1,4 +1,4 @@
-error: return_raw functions must return Result<T, Box<EvalAltResult>>
+error: functions marked with 'return_raw' must return Result<Dynamic, Box<EvalAltResult>>
   --> $DIR/export_mod_raw_noreturn.rs:12:5
    |
 12 | pub fn test_fn(input: &mut Point) {

codegen/ui_tests/rhai_fn_getter_signature.stderr

@@ -1,4 +1,4 @@
-error: property getter requires exactly 1 argument
+error: property getter requires exactly 1 parameter
   --> $DIR/rhai_fn_getter_signature.rs:13:9
    |
 13 |     pub fn test_fn(input: Point, value: bool) -> bool {

codegen/ui_tests/rhai_fn_index_getter_signature.stderr

@@ -1,4 +1,4 @@
-error: index getter requires exactly 2 arguments
+error: index getter requires exactly 2 parameters
   --> $DIR/rhai_fn_index_getter_signature.rs:13:9
    |
 13 |     pub fn test_fn(input: Point) -> bool {

codegen/ui_tests/rhai_fn_setter_index_signature.stderr

@@ -1,4 +1,4 @@
-error: index setter requires exactly 3 arguments
+error: index setter requires exactly 3 parameters
   --> $DIR/rhai_fn_setter_index_signature.rs:13:9
    |
 13 |     pub fn test_fn(input: Point) -> bool {

codegen/ui_tests/rhai_fn_setter_signature.stderr

@@ -1,4 +1,4 @@
-error: property setter requires exactly 2 arguments
+error: property setter requires exactly 2 parameters
   --> $DIR/rhai_fn_setter_signature.rs:13:9
    |
 13 |     pub fn test_fn(input: Point) -> bool {