Add pretty printing to more sql constructs

[lovasoa]

This is a followup on #1847

Here are some constructs that are currently not handled by the pretty printer (they are displayed on a single line). I'm opening this to serve as a tracking issue to track implementation of these.

• Format INSERT INTO with both VALUES and SELECT forms
• Support UPDATE and DELETE with proper clause indentation
• indent CREATE TABLE column definitions and constraints
• Format CREATE VIEW and nested SELECT cleanly
• Handle CREATE FUNCTION/PROCEDURE blocks with inner SQL formatting
• format json_table and xmltable
• Format BEGIN, COMMIT, ROLLBACK blocks clearly
• Support control flow structures (IF, WHILE, LOOP) with block indentation
• support multiline strings (the indentation should not be reflected inside the string)
• Handle MERGE statements with WHEN MATCHED and WHEN NOT MATCHED branches
• format CREATE INDEX with minimal structure
• Handle EXPLAIN, EXPLAIN ANALYZE, and DESCRIBE statements

cc @alamb