[MCR] RevisionStore, enable insertions for new schema

[MCR] RevisionStore, enable insertions for new schema

Enable inserts to the new MCR db schema in single slot mode only.

TODO:
 - RELEASE NOTES

Notes:
 - When in MIGRATION_WRITE_NEW or greater, deleting and then
 restoring a page will result in different data in the revision table.
 For example, if you delete a page that has text_ids present in the
 revision table and restore it, the text_ids will be blank after.
 - When in MIGRATION_WRITE_BOTH or greater the archive table will
 start to ar_content_model entries where previously it would have been
 given NULL. This is due to the old content schema having NULL in the db
 when the default content model is used, but the new schema will always
 have a value, taken from the content_models table

Note: If259b1e1c49ce was squashed into this change.

Bug: T183488
Bug: T174024
Change-Id: Ic2221da30c8f6ac2ba42720fcd568f2d0ed70534