Add rust_test and rust_test_host.

* Rust tests are like binary files compiled with --test.
  New test.go follows binary.go code patterns and reuses
  some code in binary.go.
* Generate one test per source file as testPerSrc in cc/test.go.
  The "all tests" variation feature of cc/test.go is not copied yet.
  Fix some Stem and SubName settings to make testPerSrc work.
* Move cc.CheckDuplicate to android.CheckDuplicate,
  which is now shared by cc and rust.
* Refactor tests in binary_test.go and add new test_test.go.

Bug: 140938178
Test: mm in rust projects, added rust_test and rust_test_host
Change-Id: Ia6fec8b4cf2572fd352ab1938a1f3c7b5cca2212
diff --git a/rust/rust.go b/rust/rust.go
index ce81b91..ec3b590 100644
--- a/rust/rust.go
+++ b/rust/rust.go
@@ -39,6 +39,7 @@
 	android.RegisterModuleType("rust_defaults", defaultsFactory)
 	android.PreDepsMutators(func(ctx android.RegisterMutatorsContext) {
 		ctx.BottomUp("rust_libraries", LibraryMutator).Parallel()
+		ctx.BottomUp("rust_unit_tests", TestPerSrcMutator).Parallel()
 	})
 	pctx.Import("android/soong/rust/config")
 }
@@ -58,6 +59,7 @@
 	AndroidMkProcMacroLibs []string
 	AndroidMkSharedLibs    []string
 	AndroidMkStaticLibs    []string
+	SubName                string `blueprint:"mutated"`
 }
 
 type Module struct {
@@ -495,9 +497,10 @@
 }
 
 var (
-	rlibDepTag      = dependencyTag{name: "rlibTag", library: true}
-	dylibDepTag     = dependencyTag{name: "dylib", library: true}
-	procMacroDepTag = dependencyTag{name: "procMacro", proc_macro: true}
+	rlibDepTag       = dependencyTag{name: "rlibTag", library: true}
+	dylibDepTag      = dependencyTag{name: "dylib", library: true}
+	procMacroDepTag  = dependencyTag{name: "procMacro", proc_macro: true}
+	testPerSrcDepTag = dependencyTag{name: "rust_unit_tests"}
 )
 
 func (mod *Module) depsToPaths(ctx android.ModuleContext) PathDeps {