Add a tool to merge two partial OTAs

Some partners have large number of products that share common
images. Generating OTAs for all these products waste a lot of CPU
cycles, because we waste time diffing the same images multiple times.
To mitigate this, add a tool for merging partial OTAs. Partners can
generate a partial OTA for common images, and re-use the generated OTA
by merging with each product specific OTA.

Bug: 227848550
Test: Run merge_otas.py on 4 OTAs, install the generated OTA

Change-Id: Ie38d522cdc9b89b1123b3d8190516c3648f99788
diff --git a/tools/releasetools/Android.bp b/tools/releasetools/Android.bp
index 8063ae2..e2173e4 100644
--- a/tools/releasetools/Android.bp
+++ b/tools/releasetools/Android.bp
@@ -150,8 +150,6 @@
         "edify_generator.py",
         "non_ab_ota.py",
         "ota_from_target_files.py",
-        "ota_utils.py",
-        "payload_signer.py",
         "target_files_diff.py",
     ],
     libs: [
@@ -161,6 +159,7 @@
         "releasetools_verity_utils",
         "apex_manifest",
         "care_map_proto_py",
+        "ota_utils_lib",
     ],
     required: [
         "brillo_update_payload",
@@ -325,6 +324,33 @@
     ],
 }
 
+python_library_host {
+    name: "ota_utils_lib",
+    srcs: [
+        "ota_utils.py",
+        "payload_signer.py",
+    ],
+}
+
+python_binary_host {
+    name: "merge_ota",
+    version: {
+        py3: {
+            embedded_launcher: true,
+        },
+    },
+    srcs: [
+        "merge_ota.py",
+    ],
+    libs: [
+        "ota_metadata_proto",
+        "update_payload",
+        "care_map_proto_py",
+        "releasetools_common",
+        "ota_utils_lib",
+    ],
+}
+
 python_binary_host {
     name: "build_image",
     defaults: [
@@ -545,6 +571,7 @@
         "sign_apex.py",
         "sign_target_files_apks.py",
         "validate_target_files.py",
+        "merge_ota.py",
         ":releasetools_merge_sources",
         ":releasetools_merge_tests",
 
@@ -561,6 +588,7 @@
         "releasetools_img_from_target_files",
         "releasetools_ota_from_target_files",
         "releasetools_verity_utils",
+        "update_payload",
     ],
     data: [
         "testdata/**/*",