Validate monolithic and modular hidden API flags are consistent

This makes sure that where there is overlap between the hidden API
flags generated for a module and the monolithic flags that they are
identical. That ensures that the modular hidden API flags will be
compatible with previous releases that relied on the monolithic flags.

Bug: 179354495
Test: m out/soong/.intermediates/art/build/boot/art-bootclasspath-fragment/android_common_apex10000/modular-hiddenapi/all-flags.csv
      m out/soong/hiddenapi/hiddenapi-flags.csv
      - Create some inconsistencies between the above two files.
      m out/soong/hiddenapi/hiddenapi-flags.csv.valid
Change-Id: Iaf9e23cef63e221608955d89dc8d496bcc70c86e

scripts/hiddenapi/Android.bp

@@ -47,3 +47,18 @@ python_binary_host {
         },
     },
 }
+
+python_binary_host {
+    name: "verify_overlaps",
+    main: "verify_overlaps.py",
+    srcs: ["verify_overlaps.py"],
+    version: {
+        py2: {
+            enabled: false,
+        },
+        py3: {
+            enabled: true,
+            embedded_launcher: true,
+        },
+    },
+}