Adds CREATE SEQUENCE and DROP SEQUENCE

[Hydrocharged]

Companion PR:

• Added additional function to RootValue dolt#7848

This adds functionality for CREATE SEQUENCE and DROP SEQUENCE. For sequences, this is what is in the PR:

• MINVALUE
• MAXVALUE
• INCREMENT
• AS DATA TYPE
• START WITH
• CYCLE

This is what is missing:

• TEMPORARY
• UNLOGGED
• CACHE
• OWNED BY
• SERIAL
• Merging
• Table Querying

Of what's missing, merging and SERIAL are the main additions, with OWNED BY required for proper SERIAL support. Table querying is fairly straightforward (the pg_sequences system table, etc.). The others are, hopefully, unnecessary for now and can be postponed, although perhaps we can save the CACHE value and ignore it since it's primarily a performance-oriented option.

With that, SERIAL and merging will come in the next PR, since this is already very large. Also of note, the Writer and Reader utilities were implemented for my Convert-to-Cast PR but they were useful here, so I pulled them from that in-flight PR and added them here.

[zachmu]

Mostly looks good.

Main comment is to use flatbuffers for serialization, don't roll your own.