Move fsverity metadata generation to Makefile

build_image.py has been handling fsverity metadata generation in the
packing step, but it can cause issues because the metadata files are
missing in the $OUT directory, and they only exist in result system.img.
This change moves the generation logic into Makefile, and makes the
metadata tracked by ninja graph.

Bug: 206326351
Test: PRODUCT_SYSTEM_FSVERITY_GENERATE_METADATA := true and build
Change-Id: I1f910d8ac6e2cc3c54f35916871733c632f18e44
diff --git a/tools/releasetools/Android.bp b/tools/releasetools/Android.bp
index bf7f9a0..f3123b2 100644
--- a/tools/releasetools/Android.bp
+++ b/tools/releasetools/Android.bp
@@ -554,12 +554,25 @@
 }
 
 python_binary_host {
-    name: "fsverity_metadata_generator",
+    name: "fsverity_manifest_generator",
     srcs: [
-        "fsverity_metadata_generator.py",
+        "fsverity_manifest_generator.py",
     ],
     libs: [
         "fsverity_digests_proto_python",
+        "releasetools_common",
+    ],
+    required: [
+        "aapt2",
+        "apksigner",
+        "fsverity",
+    ],
+}
+
+python_binary_host {
+    name: "fsverity_metadata_generator",
+    srcs: [
+        "fsverity_metadata_generator.py",
     ],
     required: [
         "fsverity",