java_sdk_library: Extract common stubs redirect code

The java_sdk_library and java_sdk_library_import redirect a request for
header and implementation jars to broadly the same place although the
java_sdk_library does have some special code that is mixed in with the
common code.

This change separates the java_sdk_library special code from the common
code and moves the common code into its own method for use by both
module types. That makes the special behavior clearer and ensures the
common behavior remains consistent in future.

Test: m nothing
Bug: 155164730
Merged-In: I53e41a18792488aefd6a886c587559e90b3c4fde
Change-Id: I53e41a18792488aefd6a886c587559e90b3c4fde
(cherry picked from commit b05d4295)