Update 1.x to Laravel 8 and minimum PHP to 7.3

[joshuafredrickson]

This bumps the 1.x branch to Laravel 8 from 7, also increasing the minimum PHP version to 7.3.

This specifically addresses compatibility with newer versions of log1x/acf-composer as it uses Str::remove, which was introduced in Laravel 8.41.0.

Ref: https://github.com/Log1x/acf-composer/blob/33e2b7529fbd7190f024dd3d66a6e9a2b95e6f5b/src/AcfComposer.php#L91 Ref: https://github.com/laravel/framework/releases/tag/v8.41.0

[joshuafredrickson]

I've been thinking on this for a minute, and you're right. Probably the best path forward is to take a serious look into updating the v1 sites at some point. I don't have the bandwidth to test PHP 7.2 or 7.3 in this context either.

@Log1x addressed this issue in acf-composer, which was my main reason for submitting this PR. 👍 Not to say that there aren't other compatibility issues that will arise in other situations.

I have about 4-5 sites that are currently on v1 that I can use to test migration paths moving forward. In the interim, I'll post on Discourse to see if anyone has experience migrating from v1 to v2.