Implement FilePackage class

This is another implementation of the Package class. And we will later
need it when reading the package from FUSE.

Bug: 127071893
Test: unit tests pass, sideload a file package on sailfish
Change-Id: I3de5d5ef60b29c8b73517d6de3498459d7d95975
diff --git a/tests/Android.bp b/tests/Android.bp
index 898ed7d..ef5919e 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -77,6 +77,7 @@
     "librecovery",
     "librecovery_fastboot",
     "libminui",
+    "libpackage",
     "libverifier",
     "libotautil",
 
@@ -117,6 +118,7 @@
     static_libs: libapplypatch_static_libs + [
         "librecovery_ui",
         "libminui",
+        "libpackage",
         "libverifier",
         "libotautil",
         "libupdater",