Treat `Set` as an `Array` in `Relation#where`

I do not want to set the expectation that any enumerable object should
behave this way, but this case in particular comes up frequently enough
that I'm caving on this one.

Fixes #30684.

activerecord/CHANGELOG.md

@@ -1,3 +1,8 @@
*   Passing a `Set` to `Relation#where` now behaves the same as passing an
    array.

    *Sean Griffin*

*   Use given algorithm while removing index from database.

    Fixes #24190.

activerecord/lib/active_record/relation/predicate_builder.rb

@@ -13,6 +13,7 @@ def initialize(table)
      register_handler(Range, RangeHandler.new(self))
      register_handler(Relation, RelationHandler.new)
      register_handler(Array, ArrayHandler.new(self))
      register_handler(Set, ArrayHandler.new(self))
    end

    def build_from_hash(attributes)

activerecord/test/cases/relations_test.rb

@@ -1912,6 +1912,19 @@ def test_relation_join_method
    end
  end

  test "#where with set" do
    david = authors(:david)
    mary = authors(:mary)

    authors = Author.where(name: ["David", "Mary"].to_set)
    assert_equal [david, mary], authors
  end

  test "#where with empty set" do
    authors = Author.where(name: Set.new)
    assert_empty authors
  end

  private
    def custom_post_relation
      table_alias = Post.arel_table.alias("omg_posts")