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

android/util.go

@@ -352,3 +352,14 @@ func ShardStrings(s []string, shardSize int) [][]string {
 	}
 	return ret
 }
+
+func CheckDuplicate(values []string) (duplicate string, found bool) {
+	seen := make(map[string]string)
+	for _, v := range values {
+		if duplicate, found = seen[v]; found {
+			return
+		}
+		seen[v] = v
+	}
+	return
+}