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
diff --git a/rust/proc_macro.go b/rust/proc_macro.go
index 1a247d9..0da87da 100644
--- a/rust/proc_macro.go
+++ b/rust/proc_macro.go
@@ -77,3 +77,10 @@
 	TransformSrctoProcMacro(ctx, srcPath, deps, flags, outputFile, deps.linkDirs)
 	return outputFile
 }
+
+func (procMacro *procMacroDecorator) getStem(ctx ModuleContext) string {
+	stem := procMacro.baseCompiler.getStemWithoutSuffix(ctx)
+	validateLibraryStem(ctx, stem, procMacro.crateName())
+
+	return stem + String(procMacro.baseCompiler.Properties.Suffix)
+}