Fixed custom validation context bug where child
associations were not being saved.

Fixes #13854.

[Eric Chahin, Aaron Nelson, & Kevin Casey]
eliminate repetition in guide links for past releases [ci skip]
passing a nil should always raise an ArgumentError
push up bind params on "simple" subquery calculations

bind parameters we not being propogated to simple subquery calculation
calls. This fixes it
make `db:structure:load` listed with `rake -T`
passing a nil in the polymorphic array is not supported. remove nils before you call the method
Move dup destroyed test to specific file that tests dup logic

Also change other related test to use existing record rather than
creating new one.
Add branch to arel on Gemfile to allow local bundle config [ci skip]
Add missing require to fix test :bomb:
Use #include? instead of #any?, make it simpler
Test typecasting on instance rather than class itself
Merge pull request #14957 from akshay-vishnoi/test-cases

Test typecasting on instance rather than class itself
Typo, grammar and textual changes [ci skip]
Merge pull request #14956 from akshay-vishnoi/refactor

Use #include? instead of #any?, make it simpler
Merge pull request #14924 from eric-chahin/issue_13854

Fixed custom validation context bug for child associations
docs, restructure newly added part to `includes`. [ci skip]

This is a follow up to #14139.

/cc @carlosantoniodasilva
Merge pull request #14952 from gregmolnar/schema_load

make `db:structure:load` listed with `rake -T`
Refactor test to not care about the specific result of valid?

Only care about its truthiness rather than asserting specific true/false
values. If we need to check for the return value in particular, there will
be a test for that.
Remove duplicated fixture addition
Reorganize ActiveRecord tasks [Arun Agrawal & Abd ar-Rahman Hamidi]