[DataStore] Introduce observer interface and provide implementation

Bug: 325144964
Test: follow up UT
Change-Id: I53bfff3c1e2dbd2f0a2304eb558c2734f34472ec
diff --git a/packages/SettingsLib/DataStore/Android.bp b/packages/SettingsLib/DataStore/Android.bp
new file mode 100644
index 0000000..c5957c6
--- /dev/null
+++ b/packages/SettingsLib/DataStore/Android.bp
@@ -0,0 +1,15 @@
+package {
+    default_applicable_licenses: ["frameworks_base_license"],
+}
+
+android_library {
+    name: "SettingsLibDataStore",
+    defaults: [
+        "SettingsLintDefaults",
+    ],
+    srcs: ["src/**/*"],
+    static_libs: [
+        "androidx.annotation_annotation",
+        "androidx.collection_collection-ktx",
+    ],
+}