Generate genrule modules for merged api txts

Add a soong plugin that can generate the genrule definitions for the
merged api txt files. This will allow removing a lot of duplicated
lists in the Android.bp and simplify adding new modules.

Bug: 169103987
Test: follow-up that uses these rules (branch dependent)
Change-Id: I0c7a9921b7f4c5b74f8b652cb357abf9444ce93f

api/Android.bp

@@ -24,6 +24,19 @@ package {
     default_applicable_licenses: ["frameworks_base_license"],
 }
 
+bootstrap_go_package {
+    name: "soong-api",
+    pkgPath: "android/soong/api",
+    deps: [
+        "blueprint",
+        "soong",
+        "soong-android",
+        "soong-genrule",
+    ],
+    srcs: ["api.go"],
+    pluginFor: ["soong_build"],
+}
+
 python_defaults {
     name: "python3_version_defaults",
     version: {