sql: block FKs to/from TTL tables

[otan]

This table blocks FKs to and from TTL tables. Note the RFC previously
only said to, but I actually thought of a new case and decided that is
was probably prudent to block this both ways. RFC is reflected
accordingly.

Release note: None

[cockroach-teamcity]

This change is 

[rafiss]

lgtm!

though similar to my comment on the other PR, have we already considered blocking computed columns and partial index defs? (this would be for a future PR)

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @otan and @rafiss)

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-- commits, line 5 at r1:
nit: missed phrasing after "only said to"

[otan]

have we already considered blocking computed columns and partial index defs?

i think we're ok here since:
(a) dropColumn knows how to handle if these exist
(b) with strict filtering these can be ignored, similar to a normal table lookup

TFTR!
bors r+

[rafiss]

i guess it's an even more general question - do computed columns and partial index defs already play nice with DEFAULT/ON UPDATE columns? i think we might have an issue for that somewhere actually..

[craig]

Build succeeded:

• GitHub CI (Cockroach)