Introduce a java_system_features_srcs wrapper for codegen

Use soong to aggregate all system feature-related build flags as input
to the existing system feature codegen tool. Use this instead of the
more clumsy raw genrule variant. This is an effective no-op in terms of
generated code or framework impact, but should improve maintainability.

Test: m --no-skip-soong-tests
Bug: 203143243
Change-Id: I67158dd6f0454556f8d75685cfc86a68b3e47089
diff --git a/systemfeatures/Android.bp b/systemfeatures/Android.bp
new file mode 100644
index 0000000..a65a6b6
--- /dev/null
+++ b/systemfeatures/Android.bp
@@ -0,0 +1,18 @@
+package {
+    default_applicable_licenses: ["Android-Apache-2.0"],
+}
+
+bootstrap_go_package {
+    name: "soong-systemfeatures",
+    pkgPath: "android/soong/systemfeatures",
+    deps: [
+        "blueprint",
+        "blueprint-proptools",
+        "soong",
+        "soong-android",
+        "soong-java",
+    ],
+    srcs: ["system_features.go"],
+    testSrcs: ["system_features_test.go"],
+    pluginFor: ["soong_build"],
+}