apex: set ":vndk" as required for vendor apexes

When a vendor APEX sets use_vndk_as_stable: true, then the apex doesn't
bundle VNDK libraries but instead it uses them from the "vndk" namespace
at runtime.

":vndk" is a pseudo-name for VNDK libraries, which is processed by
linkerconfig so that the generated linker configuration allows the
namespace for the apex to access VNDK libs.

Bug: 159576928
Test: test with a test-only vendor apex
      it runs okay with VNDK libs. (lsof shows that it opens libs from
      VNDK APEX)
Change-Id: I924ce0fea696162575f59589b8f858deddf436b3

apex/apex_test.go

@@ -2201,6 +2201,10 @@ func TestVendorApex(t *testing.T) {
 	data.Custom(&builder, name, prefix, "", data)
 	androidMk := builder.String()
 	ensureContains(t, androidMk, `LOCAL_MODULE_PATH := /tmp/target/product/test_device/vendor/apex`)
+
+	apexManifestRule := ctx.ModuleForTests("myapex", "android_common_myapex_image").Rule("apexManifestRule")
+	requireNativeLibs := names(apexManifestRule.Args["requireNativeLibs"])
+	ensureListNotContains(t, requireNativeLibs, ":vndk")
 }
 
 func TestVendorApex_use_vndk_as_stable(t *testing.T) {
@@ -2250,6 +2254,10 @@ func TestVendorApex_use_vndk_as_stable(t *testing.T) {
 		"bin/mybin",
 		"lib64/libvendor.so",
 	})
+
+	apexManifestRule := ctx.ModuleForTests("myapex", "android_common_myapex_image").Rule("apexManifestRule")
+	requireNativeLibs := names(apexManifestRule.Args["requireNativeLibs"])
+	ensureListContains(t, requireNativeLibs, ":vndk")
 }
 
 func TestAndroidMk_UseVendorRequired(t *testing.T) {