Make some Job methods public

This will allow these methods to be implemented and tested by the
upcoming UnpackJob class. Since UnpackJobTest will be written in Kotlin,
these Job methods need to be public in order to be accessed by this test
class.

Bug: 420540391
Flag: EXEMPT no functional change
Test: atest DocumentsUIGoogleTests:com.android.documentsui.services
Change-Id: Iccafd72b81d53fa096cb4e70075ae787084780e0