Check-in initial version of TextClassifierService in external/libtc

1. Move existing native codes to native folder.
2. Move existing jni java codes to jni.
3. Copy TextClassifierService java codes to java

Three build targets are introduced:
1. TextClassifierServiceLibNoManifest:All the java codes without
   AndroidManifest, will be used by ExtServices.
2. TextClassifierServiceLib: All the java codes with AndroidManifest,
   used by our test and our own APK.
3. TextClassifierService: Our standalone TCS APK, mostly for our own
   testing.

Test: atest TextClassifierServiceTest
Test: Install the apk, try smart selection.
Bug: 135110855

Change-Id: I17173769bc20cc36d6d16bd8ea511ecbaac4bb5d
diff --git a/TEST_MAPPING b/TEST_MAPPING
new file mode 100644
index 0000000..2b02610
--- /dev/null
+++ b/TEST_MAPPING
@@ -0,0 +1,12 @@
+{
+  "presubmit": [
+    {
+      "name": "TextClassifierServiceTest",
+      "options": [
+        {
+          "exclude-annotation": "androidx.test.filters.FlakyTest"
+        }
+      ]
+    }
+  ]
+}
\ No newline at end of file