Move response file handling to a separate package

sbox is going to need to read and write response files, move ReadRspFile
to its own package.

Test: response_test.go
Change-Id: Iecb5486b4aaeb2531828743ad8ef784df675e18e
diff --git a/zip/Android.bp b/zip/Android.bp
index b28adbd..14541eb 100644
--- a/zip/Android.bp
+++ b/zip/Android.bp
@@ -25,6 +25,7 @@
         "android-archive-zip",
         "blueprint-pathtools",
         "soong-jar",
+        "soong-response",
     ],
     srcs: [
         "zip.go",