Load flags in framework from framework

For flags in display_flags_lib, and camera_platform_flags_core_java_lib
have been added in framework. If these flags added in system again, it
will fail test
testBootClasspathAndSystemServerClasspath_nonDuplicateClasses. Since
framework jar will always be loaded, then instead of adding the flags
via `static_libs`, if the flags exist in framework, then in system
service, the same flag can be added via `libs` for building purpose. In
the runtime, the real flag will be loaded from framework.

Bug: 301945339
Test: presubmit
Change-Id: I17f753e52e549d8ac9a7086e823be025eca1e9b2