Add arg for overwriting class loader class path

Added stored_context srgument to EncodeContextForOatFile that
overwrites the class path when non-null.

This is used by the --stored-class-loader-context argument. Fixed
the test.

Bug: 70934104
Bug: 67345922
Test: test-art-host-gtest

(cherry picked from commit c4440775)

Merged-In: If877d8cfe9d34eeaa941e9f6df2e12539d9c4a6f
Change-Id: I16fde69bad07ae173fa30dff2fcda50b000779a5