Move bionic ("runtime") apex definition into bionic/.

Bug: http://b/139176024
Test: boots
Change-Id: Ifc3829e00b99c2f65ed932f0b42ab1ae59fec27c
diff --git a/apex/manifest.json b/apex/manifest.json
new file mode 100644
index 0000000..20a8314
--- /dev/null
+++ b/apex/manifest.json
@@ -0,0 +1,4 @@
+{
+  "name": "com.android.runtime",
+  "version": 1
+}