Fix bootclasspath_fragment build failure during from-text stub build

This change enables bootclasspath_fragment module to be correctly built
during from-text stub build by android-non-updatable module to be
interpreted as its java_api_library equivalent.

Test: go test ./java
Bug: 279460171
Change-Id: Ia6b60edcb60782977cc59855f1cf5d3a46e9f682