Modify dist artifact dependency to respect the RELEASE_HIDDEN_API_EXPORTABLE_STUBS build flag

Currently, the "exportable" stubs and the api files are copied to the
dist directory during SDK builds regardless of the value of the
RELEASE_HIDDEN_API_EXPORTABLE_STUBS build flag. This change modifies
such behavior that the "exportable" artifacts are copied to the dist
directory only when the RELEASE_HIDDEN_API_EXPORTABLE_STUBS flag value
is set to true.

Test: lunch aosp_arm-trunk_staging-eng && m sdk dist and inspect ninja graph to verify that the "everything" artifacts are copied to the dist directory
Bug: 330417789
Change-Id: I3b83375610eb172d7b9da7ea831a74cd427b696c