Modify sdk_library to dist exportable api files by default

Currently, the "exportable" stubs are copied to the dist directory by
default when building the java_sdk_library module. However, "everything"
api files (current & removed) are copied to the dist directory, causing
confusion to the developers. This change modifies the default behavior
so that the "exportable" api files are copied to the dist directory and
match the behavior of the stubs.

Test: m nothing
Bug: 325639165
Change-Id: I2e3b158bb638d30629120b32aa3e88bb26231020