Add bootclasspath_fragment.

Note that the contents of the bootclasspath_fragment are added as
dependencies to an apex, so there is no need to duplicate them in
java_libs.

Bug: 180105615
Test: atest CtsClasspathsTestCases
Change-Id: Idf501d35b631782d6c0b6eed6f6063cfb332d8e6

apex/appsearch/Android.bp

@@ -24,8 +24,8 @@ package {
 apex {
     name: "com.android.appsearch",
     manifest: "apex_manifest.json",
+    bootclasspath_fragments: ["com.android.appsearch-bootclasspath-fragment"],
     java_libs: [
-        "framework-appsearch",
         "service-appsearch",
     ],
     key: "com.android.appsearch.key",
@@ -45,3 +45,10 @@ android_app_certificate {
     // com.android.appsearch.pk8 (the private key)
     certificate: "com.android.appsearch",
 }
+
+// Encapsulate the contributions made by the com.android.appsearch to the bootclasspath.
+bootclasspath_fragment {
+    name: "com.android.appsearch-bootclasspath-fragment",
+    contents: ["framework-appsearch"],
+    apex_available: ["com.android.appsearch"],
+}