Support more ALTER TABLE operations #329

Related umbrella: #130

Current state

ALTER TABLE only supports a narrow subset of operations.

Missing pieces include:

• multiple actions in one statement
• ALTER COLUMN TYPE USING
• add/drop constraints
• rename table
• more position / option variants

Expected

Support more ALTER TABLE operations and variants.

Pointers

• src/binder/mod.rs:508
• src/binder/alter_table.rs:143
• src/binder/alter_table.rs:197