Enforce correct rust library file names.

rustc expects libraries and proc_macro filenames to conform to
a particular format, alphanumeric with underscores and lib${crate_name}.*.
Enforce this with a check when getStem() is called.

This makes the crate_name property required for proc_macros and
libraries. This also removes the notion of a default crate name derived
from the module name. It's not needed for binaries, so this won't impact
them.

Bug: 143579265
Test: m -j crosvm.experimental
Change-Id: I2770cf7d02dd4291c3d240d58d242b940098dcee

rust/rust.go

@@ -225,11 +225,7 @@ func DefaultsFactory(props ...interface{}) android.Module {
 }
 
 func (mod *Module) CrateName() string {
-	if mod.compiler != nil && mod.compiler.crateName() != "" {
-		return mod.compiler.crateName()
-	}
-	// Default crate names replace '-' in the name to '_'
-	return strings.Replace(mod.BaseModuleName(), "-", "_", -1)
+	return mod.compiler.crateName()
 }
 
 func (mod *Module) CcLibrary() bool {