Revert "Partial Revert "Populate individual classpath_fragments'..."

Revert submission 14717811-revert-populate-platform-bootclasspath

Reason for revert: retry with a fix
Reverted Changes:
Ib58cd0211:Revert "Add bootclasspath_fragments to platform-bo...
I13b622d6c:Partial Revert "Populate individual classpath_frag...

Bug: 180105615
Test: atest sdkextensions_e2e_tests

Change-Id: I7b6b6b980a4c6430a70394e85222f3b35c4efd5f