Merge pull request #16006 from ShunsukeAida/xml_http_request_comment_change

[ci skip] Fixed the documentation of xml_http_request? (aka xhr?)
flash doesn't pass objects #15522 [ci skip]
Add regression tests for keys on nested associations

This adds the regressions tests from issue #15893 to
master. It's checking that both strings and symbols are
accepted as keys for nested associations.
Merge pull request #15999 from eileencodes/add-regression-tests-for-keys-on-nested-associations

Add regression tests for keys on nested associations
Improve token_and_options regex and test

add a test case to test the regex for the helper method raw_params
do not hold on to a stale connection object. fixes #15998
Tiny follow-up to #15987 and 088b4c3e [ci skip]
Revert "Merge pull request #15394 from morgoth/fix-automatic-maintaining-test-schema-for-sql-format"

This reverts commit 46139d33c06715e74ad450428ece3ee84da98579, reversing
changes made to 8f247871bb18b2e3036a05df5f62cbfe3b402586.

Conflicts:
	activerecord/CHANGELOG.md
Move pk initialization logic onto `AttributeSet`

Better encapsulates its internals from `ActiveRecord::Base`.
Don't error when `dup`ing a record with no PK
Merge pull request #16007 from nishantmodak/flash_msg_as_string

flash doesn't pass objects #15522 [ci skip]
Merge pull request #16016 from sgrif/sg-dup

Don't error when `dup`ing a record with no PK
Fix typo
[ci skip] Changes some wording to better foreshadow what is coming up later.
This should prevent some anxiety readers may experience when the doc goes into something different than what it just explained. Also clarifies a statement about priority in engines and application environments

[ci skip] fixes double `the`

[ci skip] more clarifications

[ci skip] changes from tics to quotes
Fix SQL injection when querying against ranges and bitstrings

Fix CVE-2014-3483 and protect against CVE-2014-3482.
Quote range strings when quoting PG ranges

The test case for CVE-2014-3483 doesn't actually send the generated SQL
to the database. The generated SQL is actually invalid for real inputs.
Merge pull request #16022 from sgrif/sg-range-quoting

Quote range strings when quoting PG ranges
Merge pull request #16015 from sgrif/sg-ensure-initialized

Move pk initialization logic onto `AttributeSet`

Conflicts:
	activerecord/lib/active_record/attribute_set.rb
automatically include ActiveModel::Validations when include ActiveModel::SecurePassword
Merge pull request #16024 from aditya-kapoor/include-validations

automatically include ActiveModel::Validations when include ActiveModel::SecurePassword