Add java_sdk_library in bootclasspath_fragment contents to sdk

A java_library specified in a bootclasspath_fragment's contents
property will be automatically added to the sdk containing that
bootclasspath_fragment. Previously, if that was attempted with a
java_sdk_library it would be added to the sdk as if it was a normal
java_boot_libs which would prevent the sdk from containing the
API specific artifact such as current.txt files and stub libraries
and sources.

This change fixes that and adds a java_sdk_library as a java_sdk_libs
module.

Bug: 177892522
Test: m nothing
Change-Id: Ided57b846ce5b8940c7e898c786fd77602582ea2