Because the WAL relies on the tsm1.Value type, we move that into its own
tsm1/value package and set up some aliases forwarding them into tsm1. This
also required adding some methods and changing consumers to avoid the
unexported fields. I imagine this step will be useful one day when we make
the write path more efficient with respect to consuming points.
This commit additionally fixes some issues with generation. The iterator.tmpldata
and generation for array_cursor_* were removed accidentally when removing
iterators, making those generated files stale. Restore that and regenerate.
No change in functionality.