Add derive_sdk binary for reading sdk protos

Put the lowest seen number in a persist sysprop.

Bug: 137191822
Test: manual ran derive_sdk on device with fake protos installed
Change-Id: Ic73d615d9d60769d237aa5a72dae2dfe56463007
diff --git a/apex/sdkext/Android.bp b/apex/sdkext/Android.bp
index b8dcb90..12d6b86 100644
--- a/apex/sdkext/Android.bp
+++ b/apex/sdkext/Android.bp
@@ -15,7 +15,9 @@
 apex {
     name: "com.android.sdkext",
     manifest: "manifest.json",
+    binaries: [ "derive_sdk" ],
     java_libs: [ "framework-sdkext" ],
+    prebuilts: [ "com.android.sdkext.ldconfig" ],
     key: "com.android.sdkext.key",
     certificate: ":com.android.sdkext.certificate",
 }
@@ -30,3 +32,10 @@
     name: "com.android.sdkext.certificate",
     certificate: "com.android.sdkext",
 }
+
+prebuilt_etc {
+    name: "com.android.sdkext.ldconfig",
+    src: "ld.config.txt",
+    filename: "ld.config.txt",
+    installable: false,
+}