Set default visibility to private

Takes advantage of a new mechanism for specifying the default visibility
of all modules in a package to restrict the visibility of libcore
modules as much as possible:
  package {default_visibility: ["//visibility:private"]}

Bug: 133290645
Bug: 134379140
Test: m droid
Change-Id: I2ba1a6131993d218fd65cd4a8f0ad29a7a83df14
13 files changed