Soong package structure refactoring

Give prebuilt_etc and sh_binary their own packages and split the
gigantic main Android.bp up to small, per-package ones.

Test: m nothing, TreeHugger
Bug: 156980228
Change-Id: I7b00cd344b9f16861f1ff39edf0029f016b853d0

python/Android.bp

@@ -0,0 +1,24 @@
+bootstrap_go_package {
+    name: "soong-python",
+    pkgPath: "android/soong/python",
+    deps: [
+        "blueprint",
+        "soong-android",
+        "soong-tradefed",
+    ],
+    srcs: [
+        "androidmk.go",
+        "binary.go",
+        "builder.go",
+        "defaults.go",
+        "installer.go",
+        "library.go",
+        "proto.go",
+        "python.go",
+        "test.go",
+    ],
+    testSrcs: [
+        "python_test.go",
+    ],
+    pluginFor: ["soong_build"],
+}