Add test apex for sdkextensions

Because the tests build for 64-bit but run on 32-bit, this
requires adding a variant of derive_sdk that uses prefer32.

This apex has an SDK level of 45, which is verified in the
test. Also trigger the e2e test on changes to the apex.

Bug: 137191822
Bug: 143937446
Test: atest sdkextensions_e2e_test
Test: m
Change-Id: I88a75b4f438004ed9425e6629666cbbae1ab0882
Merged-In: I88a75b4f438004ed9425e6629666cbbae1ab0882
(cherry picked from commit 0d2e2a076804ac40e78728914e9928c62b76cd99)
diff --git a/apex/sdkextensions/Android.bp b/apex/sdkextensions/Android.bp
index f3e2018..4c5c2b2 100644
--- a/apex/sdkextensions/Android.bp
+++ b/apex/sdkextensions/Android.bp
@@ -18,13 +18,18 @@
 
 apex {
     name: "com.android.sdkext",
-    manifest: "manifest.json",
+    defaults: [ "com.android.sdkext-defaults" ],
     binaries: [ "derive_sdk" ],
+    prebuilts: [ "cur_sdkinfo" ],
+    manifest: "manifest.json",
+}
+
+apex_defaults {
+    name: "com.android.sdkext-defaults",
     java_libs: [ "framework-sdkextensions" ],
     prebuilts: [
-      "com.android.sdkext.ldconfig",
-      "cur_sdkinfo",
-      "derive_sdk.rc",
+        "com.android.sdkext.ldconfig",
+        "derive_sdk.rc",
     ],
     key: "com.android.sdkext.key",
     certificate: ":com.android.sdkext.certificate",