Put mysql back in civicrm.settings.php template

[demeritcowboy]

Overview

Reverts #18097 which was only ever in master, to make it consistent with idea that while technically the DSN is a pear::db string, "mysql" means "use whatever works" as far as civi is concerned.

php-mysql was removed in php 7.0, but civi still converts "mysql" to "mysqli" if you have DB_DSN_MODE=='auto' (the default). This doesn't guarantee people will always have "mysql" in their settings file - I've manually updated it to mysqli before - but keeps the default consistent.

Side-note: When installing with civicrm-setup you can put "banana://" and it will still work for the install part.

Technical Details

See also a48a43c#diff-893853f109566b29f9edd6aa9b1d1523R195

[civibot]

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[eileenmcnaughton]

@totten do you agree we should actually revert this?

[demeritcowboy]

FYI I took this comment #18174 (comment) as a hint:

IMHO, it's preferable to support DSN's with the mysql:// notation - on account of the install-base, downstream+upstream installer scripts, and general aesthetics. Tying Civi's stored-configurations to mysqli:// means it'll break again whenever php.net gets tired of maintaining mysqli and PDO-MySQL concurrently.

[seamuslee001]

Merging as I think this is consistent with Tim's comment