Bootstrap - Switch default boot process. Update docs.

[totten]

cv supports two protocols for booting a full environment with CiviCRM+CMS.

CLI Flag	Implementation	Description	Customization
--level=full	Bootstrap.php	Original protocol. Adapted from civicrm-core'scivicrm.config.php. Boots Civi then CMS.	Configure CIVICRM_SETTINGS
--level=cms-full	CmsBootstrap.php	Newer protocol. Adapted from typical HTTP lifecycle. Boots CMS then Civi.	Configure CIVICRM_BOOT

With this PR, cv will prefer CmsBootstrap.php. It aims to phase-out the older Bootstrap.php. However, this is a notable policy change, and CmsBootstrap.php has not been tested as widely. The PR retains some options so that the site-builder can switch between them more easily.

Comments

• The updated README.md describes more about how to use the options.
• Every now and then, people run into issues like https://lab.civicrm.org/dev/core/-/issues/4128 -- where a subtle discrepancy between the HTTP and CLI boot causes confusion. Switching the default should reduce that kind of issue.
• CmsBootstrap ought to be better, but it hasn't been used much. And that won't change unless we make it the default. So we'll go ahead with the change. But if anyone needs a way to back out, they can set:

  export CIVICRM_SETTINGS=Auto

Technical Details

• Formally, most cv subcommands default to --level=full|cms-full. The PR changes the interpretation of full|cms-full.
• Practically, for most invocations by most users, this changes the effective default from --level=full to --level=cms-full.
• The PR builds on a few ideas that were already in there:
  • CIVICRM_BOOT already provided a way to configure the CmsBootstrap.php protocol.
  • CIVICRM_BOOT already signaled an intent to activate CmsBootstrap.php.
  • CIVICRM_SETTINGS already provided a way to configure/ the Bootstrap.php protocol.
  • Now, CIVICRM_SETTINGS also signals an intent to activate Bootstrap.php.
• The CIVICRM_BOOT and CIVICRM_SETTINGS accept a few more values than before:
  • CIVICRM_BOOT=Auto://. will activate CmsBootstrap.php and allow it to search for the CMS.
  • CIVICRM_SETTINGS=Auto will activate Bootstrap.php and allow it to search for CiviCRM.

[totten]

OK, there were a lot of failures relating to the php:boot command - because it didn't have a code-generator for --level=cms-full. This is the command that works like so:

eval(`cv php:boot`);
echo CRM_Utils_System::version();

So I added an implementation for --level=cms-full. The output looks fairly different from --level=full. Partially, that's because it takes a different approach to class-loading. (Past-Me would have been concerned about this approach, but I think it might be OK since cv.phar now uses namespace prefixing.)

It does point to another discrepancy though -- the Bootstrap populates $_CV but CmsBootstrap doesn't.

$ cv ev 'return $GLOBALS["_CV"]["ADMIN_USER"];' --level=full
"admin"
$ cv ev 'return $GLOBALS["_CV"]["ADMIN_USER"];' --level=cms-full
null

That will be a blocker - it's needed for various test-suites to work properly.

[totten]

A second issue with switching default - on Backdrop, cv http --login --user=admin ... works with --level=full but fails with --level=cms-full.