Support PHP 8.4

[rfay]

Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem?

PHP 8.4 should go into alpha before too long. It probably won't show up in deb.sury.org until a while after that. We'll probably want to provide some kind of support for it before it arrives in deb.sury.org, we've done this before in https://github.com/ddev/ddev-contrib and elsewhere. Alpha1 is scheduled for June 6, 2024

Describe your solution

Use pecl or something to provide it. Consider a short-lived add-on as well.

Describe alternatives

No response

Additional context

No response