Extract a library from create_embedded_tools.py

We'll use the extracted functions in the upcoming
Python-based reincarnation of the
//:bazel-distfile rule.

Change-Id: I5140938ae4af50f62fb695b5b96cd41f3cd939ef
PiperOrigin-RevId: 164950515

src/BUILD

diff --git a/src/BUILD b/src/BUILD
index 15b7502..d788f1f 100644
--- a/src/BUILD
+++ b/src/BUILD
@@ -122,9 +122,15 @@
     ],
 )
 
+py_library(
+    name = "create_embedded_tools_lib",
+    srcs = ["create_embedded_tools_lib.py"],
+)
+
 py_binary(
     name = "create_embedded_tools",
     srcs = ["create_embedded_tools.py"],
+    deps = [":create_embedded_tools_lib"],
 )
 
 # TODO(philwo): Clean this up, once a Bazel that can run py_binary and sh_binary