Create publicly visible apksig-all target

This is the first step in making "apksig" target export only the
public API (i.e., not export **.internal.** classes). Once this
commit lands, existing clients which need non-public classes will
switch to apksig-all target. After that, apksig target can be
made to export only public API.

Test: bazel test ...
Test: bazel build :apksig-all
Change-Id: I78a159f3f8c4baecba4147cb822b920ba45444ce
diff --git a/BUILD b/BUILD
index 915d368..e2131ec 100644
--- a/BUILD
+++ b/BUILD
@@ -10,6 +10,14 @@
     visibility = ["//visibility:public"],
 )
 
+# All of apksig library, including private API which clients are not supposed
+# to directly depend on
+java_library(
+    name = "apksig-all",
+    srcs = glob(["src/main/java/**/*.java"]),
+    visibility = ["//visibility:public"],
+)
+
 java_binary(
     name = "apksigner",
     srcs = glob([