Add genrule for the current sdk proto

This is intended to be added to all apexes exposing SDK apis. The
version can then be bumped by changing the value in a single place.
The current version is 0.

Also build this into the sdkext module.

Bug: 137191822
Test: m com.android.sdkext
Change-Id: Ic2cd92ad1d184c8a01f0bc3d4fc21deb588cb7e8
diff --git a/apex/sdkext/Android.bp b/apex/sdkext/Android.bp
index 12d6b86..b132f7e 100644
--- a/apex/sdkext/Android.bp
+++ b/apex/sdkext/Android.bp
@@ -17,7 +17,10 @@
     manifest: "manifest.json",
     binaries: [ "derive_sdk" ],
     java_libs: [ "framework-sdkext" ],
-    prebuilts: [ "com.android.sdkext.ldconfig" ],
+    prebuilts: [
+      "com.android.sdkext.ldconfig",
+      "cur_sdkinfo",
+    ],
     key: "com.android.sdkext.key",
     certificate: ":com.android.sdkext.certificate",
 }
@@ -39,3 +42,28 @@
     filename: "ld.config.txt",
     installable: false,
 }
+
+python_binary_host {
+    name: "gen_sdkinfo",
+    srcs: [
+        "derive_sdk/sdk.proto",
+        "gen_sdkinfo.py",
+    ],
+    proto: {
+        canonical_path_from_root: false,
+    },
+}
+
+gensrcs {
+    name: "cur_sdkinfo_src",
+    srcs: [""],
+    tools: [ "gen_sdkinfo" ],
+    cmd: "$(location) -v 0 -o $(out)",
+}
+
+prebuilt_etc {
+    name: "cur_sdkinfo",
+    src: ":cur_sdkinfo_src",
+    filename: "sdkinfo.binarypb",
+    installable: false,
+}