dolt_schema_diff, dolt_patch need better support for CREATE, ALTER TABLE statements

[zachmu]

MySQL CREATE TABLE statements can include schema elements e.g. indexes that Postgres statements cannot. Currently we simply omit these elements when generating the CREATE TABLE statements for Doltgres tables. But this means that the output of dolt_schema_diff and dolt_patch are incomplete for doltgres.

The simplest solution is probably to converge on the postgres restrictions, so that we emit CREATE TABLE and ALTER TABLE statements that make sense for both dialects.