Adding support for a major PHP version

Note: This is an internal developer guide for the setup-php project.

New Stable version.

• Make the new version stable on homebrew/php tap and php-builder(should be automatic on this one).

• Add stable version builds to php-builder-windows cache.

• Keep nightly version regex as previously in unix.sh till we have a PPA build cached and in windows.ps1 till we have Xdebug and PCOV snapshot builds.

• Update docs about the new version and if there are any OS support changes.

• Bump nightly and latest versions in the php-version.json config file.

• Bump the default inputs in scripts for version.

• Bump the default version in actions.yml.

• Audit extension/tools support for the new version.

• Update tests workflows in test-setup-php.

New Nightly version

• Add build config to php/web-rmtools for the new version.

• Add builds to homebrew/php tap, php-builder and php-builder-windows.

• Update tests workflows in test-setup-php.