Set min_sdk_version to be part of mainline modules

Modules contributing mainline modules (APK/APEX) should set
min_sdk_version as well as apex_available.

For now setting min_sdk_version doesn't change build outputs.
But build-time checks will be added soon.

Bug: 152655956
Test: m
Change-Id: Ifea5ed988fad2e0d29271e6e9cbf0e12100b37d9
diff --git a/libs/nativewindow/Android.bp b/libs/nativewindow/Android.bp
index 55400c7..894f45a 100644
--- a/libs/nativewindow/Android.bp
+++ b/libs/nativewindow/Android.bp
@@ -25,6 +25,7 @@
     name: "libnativewindow_headers",
     export_include_dirs: ["include"],
     vendor_available: true,
+    min_sdk_version: "29",
 }
 
 ndk_library {