Convert rust to use ModuleProxy.

Bug: 377723687
Test: Unit tests and compare the ninja and mk files generated.
Change-Id: I2eb0134bb727f5875d579dae1fff5b70658bd2bb
diff --git a/rust/bindgen.go b/rust/bindgen.go
index 898e792..8accd03 100644
--- a/rust/bindgen.go
+++ b/rust/bindgen.go
@@ -309,7 +309,8 @@
 
 	var cmd, cmdDesc string
 	if b.Properties.Custom_bindgen != "" {
-		cmd = ctx.GetDirectDepWithTag(b.Properties.Custom_bindgen, customBindgenDepTag).(android.HostToolProvider).HostToolPath().String()
+		m := ctx.GetDirectDepProxyWithTag(b.Properties.Custom_bindgen, customBindgenDepTag)
+		cmd = android.OtherModuleProviderOrDefault(ctx, m, android.HostToolProviderInfoProvider).HostToolPath.String()
 		cmdDesc = b.Properties.Custom_bindgen
 	} else {
 		cmd = "$bindgenCmd"