colexec: fix remapping of indexed vars in filter expressions

[yuzefovich]

Previously, the remapping of indexed variables was done incorrectly
(the range for indices was too small which would cause the "custom"
ordinal of the form '@#[d]+' to keep the pound sign). Now this is
fixed.

Fixes: #41407.

Release note: None

[cockroach-teamcity]

This change is 

[yuzefovich]

Still, the current way of remapping the variables is problematic - in some cases (when a sequence of symbols @# is already present in the original filter expression), we might return incorrect results. For example, if we have a filter like @1 = '@#1', and we're doing remapping such that @1 is first replaced with @#1, then we will replace both of @#1 with @1 which will make our filter as @1 = '@1'. I don't know how to fix it though :/ Any ideas?

[yuzefovich]

I guess, maybe the correct way to handle this situation is not do the remapping (i.e. the modification) of the expression at all, but rather use a custom IVarContainer that will handle the redirection when evaluating the datums?

[yuzefovich]

Replaced by #42198.