Fix polymorphic belongs_to to correctly use parent's query_constraints

[fatkodima]

Fixes #50315.

For polymorphic association with query constraints, we get incorrect value for primary key (specifically, "id" in the referenced issue) here

rails/activerecord/lib/active_record/reflection.rb

Lines 870 to 882 in 5c4a7a7

	def association_primary_key(klass = nil)
	if primary_key = options[:primary_key]
	@association_primary_key ||= -primary_key.to_s
	elsif !polymorphic? && ((klass || self.klass).has_query_constraints? || options[:query_constraints])
	(klass || self.klass).composite_query_constraints_list
	elsif (klass || self.klass).composite_primary_key?
	# If klass has composite primary key of shape [:<tenant_key>, :id], infer primary_key as :id
	primary_key = (klass || self.klass).primary_key
	primary_key.include?("id") ? "id" : primary_key
	else
	primary_key(klass || self.klass)
	end
	end

which then incorrectly matches with foreign key (specifically, ["tenant_id", "commentable_id"] in the referenced issue) here

rails/activerecord/lib/active_record/associations/association_scope.rb

Lines 58 to 63 in 5c4a7a7

	def last_chain_scope(scope, reflection, owner)
	primary_key = Array(reflection.join_primary_key)
	foreign_key = Array(reflection.join_foreign_key)
	table = reflection.aliased_table
	primary_key_foreign_key_pairs = primary_key.zip(foreign_key)

With this change, association_primary_key now correctly returns ["tenant_id", "id"].

[eileencodes]

Hrm, I originally added the !polymorphic? check because klass can't always be computed on those associations, but this seems to be working fine based on the tests.

[eileencodes]

Thanks @fatkodima - I backported this to 7-1-stable in 59e72b0