Detect column collation mismatch while creating joins

[tznind]

Is your feature request related to a problem? Please describe.
If when creating a join (either JoinInfo or Lookup) then report any mismatch in column collations as a warning in the creation screen.

See also the work done in #1332 . We should reuse the logic there and make sure no duplication.

[tznind]

This is particularly annoying because you cannot edit an existing Lookup easily and instead have to delete and recreate it (same for JoinInfos).