Views Support Work for GA

[harshit-gangal]

View support was added in v18 with #11559 as experimental.

There are some rough edges we can resolve and call it a GA feature.

VTGate:

• Enable views by default - Views: VTGate changes for seamless integration #17439
• Create/Update View: Look only for tables involved in the select query to determine the keyspace involved rather than the plan output as plan can have multi keyspace access (lookup table) - Views: VTGate changes for seamless integration #17439
• Merge logic for drop view - Views: VTGate changes for seamless integration #17439
• Global Routing for views Views global routing #17633
• Unsharded views: preserve the view table Views global routing #17633
• Use CTEs instead of derived tables
• Flags deprecation in v23

Change to make feature seamless

1. VTTablet sends tables and views list separately i.e Views tracking on default
2. VTGate' schema tracking to store views and tables information based on keyspace being sharded or unsharded.
   • Sharded: Views statement is stored
   • Unsharded: Views as Table is stored

This will require 2 release to complete.
v22 - It will contain the VTGate side changes
v23 - VTTablet to always send views and tables separately.