Support altering columns in SQLite migrations by RENAME-ADD-UPDATE-DROP

[Rongronggg9]

Since 7bcf9b2, dropping columns in SQLite migrations is possible. We may further support altering columns in SQLite by:

ALTER TABLE "foo" RENAME COLUMN "bar" TO "bar_random_string";
ALTER TABLE "foo" ADD "bar" NEW_TYPE NOT NULL  DEFAULT "baz" /* comment */;
-- Do not CAST(x as JSON): https://gerrit.sqlalchemy.org/c/sqlalchemy/alembic/+/2011
UPDATE "foo" SET "bar" = CAST("bar_random_string" as NEW_TYPE);
ALTER TABLE "foo" DROP COLUMN "bar_random_string";

[UpstreamData]

+1. Would love to see this, mainly for migrating fields to allow null.