Create composd skeleton

This has all the scaffolding/boilerplate to create a composd service
which can be started and serve a binder interface, but with no actual
implementation yet.

Bug: 186126194
Test: adb shell cmd -w android.system.composd; service starts.
Change-Id: I2ba91b36628b21210ac901525a93664473ac8460
diff --git a/compos/composd/aidl/Android.bp b/compos/composd/aidl/Android.bp
new file mode 100644
index 0000000..90c0de0
--- /dev/null
+++ b/compos/composd/aidl/Android.bp
@@ -0,0 +1,21 @@
+package {
+    default_applicable_licenses: ["Android-Apache-2.0"],
+}
+
+aidl_interface {
+    name: "android.system.composd",
+    srcs: ["android/system/composd/*.aidl"],
+    // TODO: Make this stable when the APEX becomes updatable.
+    unstable: true,
+    backend: {
+        java: {
+            apex_available: ["//apex_available:platform"],
+        },
+        rust: {
+            enabled: true,
+            apex_available: [
+                "com.android.compos",
+            ],
+        },
+    },
+}