avoid using alias in generators

Ruby's alias produces public methods, causing a spurious Thor task
to be created.  For example, this is the reason MigrationGenerator
currently has two tasks:

    > ActiveRecord::Generators::MigrationGenerator.all_tasks.keys
    => ["singular_name", "create_migration_file"]

singular_name was meant to be an attribute, not a task.  Because it's
public, it gets called as a task every time the generator is invoked.

The fix is to ensure all generator methods have the correct
visibility.
Fix migrations with enable_extension

When using ActiveRecord::Base.table_name_prefix and/or
table_name_suffix, extension names got the same treatment as table names
when running migrations. This led to migrations that tried to call, for
example, enable_extension("prefix_hstore") on the connection.
Hash#deep_*_keys(!) recurse into nested arrays.

Following methods now recursively transform nested arrays, too.

* Hash#deep_transform_keys
* Hash#deep_transform_keys!
* Hash#deep_stringify_keys
* Hash#deep_stringify_keys!
* Hash#deep_symbolize_keys
* Hash#deep_symbolize_keys!
Verify that route constraints respond to the expected messages instead of silently failing to enforce the constraint
Check authentication scheme in Basic auth

`authenticate_with_http_basic` and its families should check the authentication
schema is "Basic".

Different schema, such as OAuth2 Bearer should be rejected by basic auth, but
it was passing as the test shows.

This fixes #10257.
Run login_procedure only when the auth_scheme is valid
Refactor AR's validations_test.rb

The `:context` switch feature is implemented in
ActiveRecord::Validations#valid? method, so we should rename the test
names, and execute `valid?` in the test.

Change test name in AR's validations_test.rb

This test is testing save method's code
Fix bugs with changed attributes tracking when transaction gets rollback
Fix Hash#deep_merge bug and improve documentation — resolves #12738

Previously merging into a hash with a falsy value would not result in
the merge-block being called. The fix is simply to check for presence
of the key in the hash.

The documentation example for `deep_merge` now appropriately
demonstrates what a deep merge does.
Fix serialized field returning serialized data after update_column
Fixes Issue #13466.

Changed the call to a scope block to be evaluated with instance_eval.
The result is that ScopeRegistry can use the actual class instead of base_class when
caching scopes so queries made by classes with a common ancestor won't leak scopes.
Stringify variables names for mysql connections

For mysql2/mysql adapters, `sql_mode` variable name set in `database.yml`
as string, was ignored and `sql_mode` was set to use strict mode.

Fixes #14895
Fixed custom validation context bug where child
associations were not being saved.

Fixes #13854.

[Eric Chahin, Aaron Nelson, & Kevin Casey]
[ci skip] Security guide clarity.
Merge pull request #14931 from heironimus/security_guide_clarity

[ci skip] Security guide clarity.
always use File.join
Merge pull request #14932 from phoet/use_file_join

always use File.join in asset_path
Merge pull request #14896 from jetthoughts/14895_overide_strict_by_sql_mode

Symbolize variables of mysql/mysql2 connection configuration

Conflicts:
	activerecord/CHANGELOG.md
never merge url options in to the first data hash

if you want options, don't mix them with the first hash, just pass them
all in with the second hash
always pass options to the _url method