Convert several unit tests from SCons to Bazel, selected from this document.

Converts the following libraries:

• change_stream_pre_image_test_helpers
• change_stream_test_helpers
• jparse_util
• update_test_helpers
• vector_clock_trivial

Converts the following unit tests:

• change_stream_pre_images_manager_test
• db_index_test
• db_op_observer_test
• db_update_test
• makeobj_spec_hash_test
• sbe_abt_test
• scripting_test
• s_query_exec_test

(more targets may be added here while the ticket is in progress)