Move assert_returns_resolved_value into helper module

This avoids re-creating the function for every assertion we make on
function return values, potentially slightly speeding up the macro
compilation.

This shouldn't make much/any difference right now because nothing
(outside of a few tests) uses resolved functions yet.

Author: bgw

turbopack/crates/turbo-tasks-macros-tests/tests/function/fail_resolved_inherent_impl.stderr

@@ -338,14 +338,7 @@ impl TurboFn {
             quote_spanned! {
                 span =>
                 {
-                    fn assert_returns_resolved_value<
-                        ReturnType,
-                        Rv,
-                    >() where
-                        ReturnType: turbo_tasks::task::TaskOutput<Return = Vc<Rv>>,
-                        Rv: turbo_tasks::ResolvedValue + Send,
-                    {}
-                    assert_returns_resolved_value::<#return_type, _>()
+                    turbo_tasks::macro_helpers::assert_returns_resolved_value::<#return_type, _>()
                 }
             }
         } else {

turbopack/crates/turbo-tasks-macros-tests/tests/function/fail_resolved_static.stderr

@@ -8,7 +8,9 @@ pub use super::{
     magic_any::MagicAny,
     manager::{find_cell_by_type, notify_scheduled_tasks, spawn_detached_for_testing},
 };
-use crate::{debug::ValueDebugFormatString, TaskInput, TaskPersistence};
+use crate::{
+    debug::ValueDebugFormatString, task::TaskOutput, ResolvedValue, TaskInput, TaskPersistence, Vc,
+};
 
 #[inline(never)]
 pub async fn value_debug_format_field(value: ValueDebugFormatString<'_>) -> String {
@@ -29,6 +31,13 @@ pub fn get_non_local_persistence_from_inputs(inputs: &impl TaskInput) -> TaskPer
     }
 }
 
+pub fn assert_returns_resolved_value<ReturnType, Rv>()
+where
+    ReturnType: TaskOutput<Return = Vc<Rv>>,
+    Rv: ResolvedValue + Send,
+{
+}
+
 #[macro_export]
 macro_rules! stringify_path {
     ($path:path) => {