LESS: Address issues in legacy library

[tbradsha]

Closes MONOREP-252

This addresses lots of warnings, deprecations, and fatals in the lessphp LESS library (https://github.com/leafo/lessphp). The library hasn't been updated in years, but it's been patched here and there to maintain compatibility.

In my edits I tried to respect the library's current style; it seems to not be linted anyway.

Proposed changes:

PHP Deprecated: Creation of dynamic property lessc::$env is deprecated in /wordpress/plugins/wpcomsh/8.1.0-alpha+rolling.1763722686.g3d7e3e4/jetpack_vendor/automattic/jetpack-mu-wpcom/src/features/custom-css/custom-css/preprocessors/lessc.inc.php on line 1892

The above (and a dozen other variants) are resolved by adding the #[\AllowDynamicProperties] attribute to the relevant classes. Were it not a copy/pasted library the better solution is to add them as properties, but this way allows us to reduce lines-of-code changes for easier comparison to the original.

PHP Deprecated: preg_match(): Passing null to parameter #4 ($flags) of type int is deprecated in /wordpress/plugins/wpcomsh/8.1.0-alpha+rolling.1763722686.g3d7e3e4/jetpack_vendor/automattic/jetpack-mu-wpcom/src/features/custom-css/custom-css/preprocessors/lessc.inc.php on line 3503
PHP Deprecated: preg_match(): Passing null to parameter #4 ($flags) of type int is deprecated in /wordpress/plugins/wpcomsh/8.1.0-alpha+rolling.1763722686.g3d7e3e4/jetpack_vendor/automattic/jetpack-mu-wpcom/src/features/custom-css/custom-css/preprocessors/lessc.inc.php on line 3534

For the above, the flags param expects an int, and null ultimately is treated as 0, so I updated them to use 0 explicitly.

PHP Warning: Trying to access array offset on false in /wordpress/plugins/wpcomsh/8.1.0-alpha+rolling.1763722686.g3d7e3e4/jetpack_vendor/automattic/jetpack-mu-wpcom/src/features/custom-css/custom-css/preprocessors/lessc.inc.php on line 665

For the above, we now make sure the key exists before trying to access its value.

PHP Fatal error: Uncaught TypeError: Unsupported operand types: string * float in /wordpress/plugins/wpcomsh/8.1.0-alpha+rolling.1763722686.g3d7e3e4/jetpack_vendor/automattic/jetpack-mu-wpcom/src/features/custom-css/custom-css/preprocessors/lessc.inc.php:1272

For the above, we cast the values to float. A non-numeric string would become 0, which then can be used in math operations.

Correction (h/t @anomiex): For the above, the keys were off by one, with $color[0] being a string that was used to determine how to process the remaining keys.

PHP Deprecated: Implicit conversion from float 22909.63671875 to int loses precision in /wordpress/plugins/wpcomsh/8.1.0-alpha+rolling.1763722686.g3d7e3e4/jetpack_vendor/automattic/jetpack-mu-wpcom/src/features/custom-css/custom-css/preprocessors/lessc.inc.php on line 1572

For the above, we cast the value to int so we can do modulo math.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

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Testing instructions:

• Go to '..'

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (WordPress.com Site Helper), and enable the fix/address_lessc_preprocessor_issues branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack-mu-wpcom-plugin fix/address_lessc_preprocessor_issues

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[github-actions]

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Code Coverage Summary

This PR did not change code coverage!

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Full summary · PHP report

[anomiex]

One thing inline, otherwise it seems reasonable.

[anomiex]

Looks reasonable