TD-13881 implement create/alter/drop/show user, create/drop/show dnode, drop database, show stables and drop table

[td-10564] 1. Enable  and then refactor the parse the nested function in select clause. 2. Add some scalar string function in function module. 3. Add more test cases.

[td-6395]<enhance>: use the keyword "every" instead of keyword of "interval" in the where clause in case of point interpolation query.