Ensure sscp jars get copied to $OUT/soong/system_server_dexjars

(This was missed in aosp/2876756, which copied only the bcp jars)

This hardcoded location is used by dex2oat to compile the dexpreopt
artifacts. The copy rules are currently generated by java_(sdk)_library
for source builds, and their prebuilt counterparts in prebuilt builds.

After this change, the copy rule will be bifurcated between source and
prebuilt builds
1. For source builds, it will come from java_(sdk)_library
2. For prebuilt builds, it will come from the top-level prebuilt apex.
   Since there can be multiple prebuilt apexes in trunk stable,
   HideFromMake will be used to determine which deapexed jar to copy.

The bifurfaction is expected to be temporary. It is needed for now since
the `apex_contributions` which will be used for source vs prebuilt
selection have not been populated completely.

Test: Added a unit test
Test: Presubmits
Test: git_master-art-host:
art-gtest (https://android-build.corp.google.com/builds/abtd/run/L40800030001459791)
Test: git_main:art_standalone_tests
(https://android-build.corp.google.com/builds/abtd/run/L09000030001463855)

Bug: 308790457

Change-Id: I3105d3b3a7e5c41cb601d07806f4ea483a61b50a