accept TableClause through mapped selectable chain

accept TableClause through mapped selectable chain

type annotation somehow decided that TableClause doesn't have
primary key fields which is not the case at all.   In particular
the "views" recipe relies on TableClause so adding a restriction
like this does not make any sense.

It seems the issue was to open this up for typing, by allowing
TableClause out as far as ddl.sort_tables() typing is passing
for now.   Support it out in get_bind() etc.

Fixes: #9071
Change-Id: If0e22e0e7df7bee0ff4b295b0ffacfbc6b7a0142