[rql2sql] Handle comparison of eid on variables from an subquery
We don't want to force using 'identity' in this case which may be easily
handled by detecting variable is a `ColumnAlias` and relation is 'eid'.
Closes #15393583
addressbook
basket
blog
book
calendar
comment
company
email
file
folder
i18ncontent
keyword
link
mailinglist
person
tag
timeseries
vcsfile