rust: Allow any host tool for custom_bindgen

Switch custom_bindgen to use any HostToolProvider
instead of just Rust modules, so any host binary can
be used as the bindgen wrapper.

Bug: 242243245
Test: presubmit
Change-Id: I9ba189b2857b3049dcf14842c178ce5846bab2f7
diff --git a/rust/bindgen.go b/rust/bindgen.go
index 96645b0..7dc1b4b 100644
--- a/rust/bindgen.go
+++ b/rust/bindgen.go
@@ -247,7 +247,7 @@
 
 	var cmd, cmdDesc string
 	if b.Properties.Custom_bindgen != "" {
-		cmd = ctx.GetDirectDepWithTag(b.Properties.Custom_bindgen, customBindgenDepTag).(*Module).HostToolPath().String()
+		cmd = ctx.GetDirectDepWithTag(b.Properties.Custom_bindgen, customBindgenDepTag).(android.HostToolProvider).HostToolPath().String()
 		cmdDesc = b.Properties.Custom_bindgen
 	} else {
 		cmd = "$bindgenCmd"