Allow `psr/log` v3 when using composer

[LeoColomb]

Alternative solution for #539. This helps to work around the issue regarding the conflicted dependencies (specifically Psr\Log package). This would allow installing the package on a PHP 8 server via Composer, while keeping the wp.org plugin a PHP 7.x target.

[!NOTE] This change requires the plugin to be published as a standard package on Packagist and then be released with a new tag. https://packagist.org/packages/submit

[!Warning] A conditional class definition is unfortunately required to match psr/log methods signatures. This is not very pretty, but, again, required. b6e81b9

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• Closes #539
• Resolves #490
• Resolves #470
• Resolves #445
• Ref #528
• Closes Cloudflare case 3130507
• Ref https://wordpress.org/support/topic/compatibility-with-php-8-2-20/
• Ref https://wordpress.org/support/topic/php-function-deprecated-php-in-8-2/
• Ref https://wordpress.org/support/topic/w3totalcache-cloudflare-extension-vs-cloudflare-apo-wordpress-plugin/
• Ref https://wordpress.org/support/topic/fatal-error-on-plugin-activation-42/
• Ref https://wordpress.org/support/topic/php-fatal-error-psrlog-php8/

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cc @Korben00

[JulienMelissas]

Would be great to get this reviewed/approved! We had a few hundred sites go down today updating Cloudflare via Composer thanks to this fun error 😅 (still trying to figure out why the error didn't show itself in staging)

[LeoColomb]

@JulienMelissas If you are a business customer of Cloudflare, don't hesitate to open an internal ticket in their support area. If so, feel free to reference our ticket 3130507.

[LeoColomb]

@aseure @jacobbednarz @william-woodhead Any possible feedback?

[tomkyser]

@aseure @jacobbednarz @william-woodhead any update? I've got a pile of duct tape getting our composer based project to work with this plugin specifically being the issue. What's holding it up?

[dev-triboo]

@aseure @jacobbednarz @william-woodhead any update?