Support PHP 7.0+

[mattstauffer]

Note: The preferred, and faster, and safer, way to use Valet if you run PHP 7.4 sites is to use PHP 8+ on the CLI, and then use Valet's site isolation to set just those sites to PHP 7.4. That's why this is more of a temporary hack than anything else.

This PR adds support for users running PHP 7.4 as their primary linked PHP as long as they still have PHP 8+ installed on their machine (as an un-linked Brew install).

Calls to valet now check if the current linked PHP version is 8+; if it isn't, valet checks whether there's a Brew-installed version of PHP that's 8+, and if so, uses those commands to run Valet.

This shouldn't introduce any lag for users with modern PHP installed, as php -r "echo phpversion();" is very fast. Users running PHP prior to 8 will see a close-to-one-second lag in all Valet commands; this way we're providing support for those users, but also encouraging those users to start using PHP 8+ and to use valet php or valet composer to proxy their calls back to the older, isolated PHP versions.

This is a hack of a fix, and may well be removed in the next major version, although at that point we may choose to keep this script but bump up the version we're checking against.

Currently tested and working on PHP 7.4, since WordPress still runs on PHP 7.4.

I'll test PHP 7.3 and 7.2, but if either require any major changes, I don't plan to support them.

• Test on PHP 7.4
• Test on PHP 8.0+ to make sure this doesn't introduce any lag
• Test on PHP 7.3
• Test on PHP 7.2
• Test on PHP 7.1
• Test on PHP 7.0