Add opt-in GDScript warning for when calling coroutine without await

modules/gdscript/tests/scripts/analyzer/warnings/missing_await.gd

@@ -0,0 +1,7 @@
+func coroutine() -> void:
+	@warning_ignore("redundant_await")
+	await 0
+
+func test():
+	await coroutine()
+	coroutine()

modules/gdscript/tests/scripts/analyzer/warnings/missing_await.out

@@ -0,0 +1,2 @@
+GDTEST_OK
+~~ WARNING at line 7: (MISSING_AWAIT) "await" keyword might be desired because the expression is a coroutine.

modules/gdscript/tests/scripts/runtime/features/await_signal_with_parameters.gd

@@ -15,11 +15,14 @@ func await_two_parameters():
 	print(result)
 
 func test():
+	@warning_ignore("missing_await")
 	await_no_parameters()
 	no_parameters.emit()
 
+	@warning_ignore("missing_await")
 	await_one_parameter()
 	one_parameter.emit(1)
 
+	@warning_ignore("missing_await")
 	await_two_parameters()
 	two_parameters.emit(1, 2)

modules/gdscript/tests/scripts/runtime/features/emit_after_await.gd

@@ -8,5 +8,6 @@ func async_func():
 	my_signal.emit()
 
 func test():
+	@warning_ignore("missing_await")
 	async_func()
 	my_signal.emit()