Convert rust module-info.json to soong

This leads to idendical results as before, with the exception of
the "required" field in module-info.json. Make has more complicated
logic to fill out the required field than soong, and it leads to
make-specific names such as ones suffixed with :32 and don't make sense
in soong. I'm don't think there are critical users of that field though,
so I'll try removing it.

Everything else should be identical to the make-generated information
though.

Bug: 389720048
Test: diff'd module-info.json before and after this cl in soong+make mode
Change-Id: I74aefe578287f07474c15e5f92a0c2780a679047
diff --git a/rust/proc_macro.go b/rust/proc_macro.go
index 28ed68b..837e1a6 100644
--- a/rust/proc_macro.go
+++ b/rust/proc_macro.go
@@ -100,3 +100,9 @@
 	// Proc_macros are never installed
 	return false
 }
+
+func (library *procMacroDecorator) moduleInfoJSON(ctx ModuleContext, moduleInfoJSON *android.ModuleInfoJSON) {
+	library.baseCompiler.moduleInfoJSON(ctx, moduleInfoJSON)
+
+	moduleInfoJSON.Class = []string{"PROC_MACRO_LIBRARIES"}
+}