Fix PHPStan level 8 issues in functions.wp-styles.php and functions.wp-scripts.php

[westonruter]

This is a subset of #10627

This PR addresses the following issues PHPStan level 8 issues:

phpstan analyze --memory-limit=4G --level=8 src/wp-includes/functions.wp-styles.php src/wp-includes/functions.wp-scripts.php

Before:

Note: Using configuration file /Users/westonruter/repos/wordpress-develop/phpstan.neon.
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 ------ --------------------------------------------------------------------------------------------------------
  Line   functions.wp-scripts.php
 ------ --------------------------------------------------------------------------------------------------------
  144    Parameter #1 $string of function trim expects string, string|null given.
         🪪  argument.type
  181    Function wp_register_script() has parameter $args with no value type specified in iterable type array.
         🪪  missingType.iterableValue
         💡  See: https://phpstan.org/blog/solving-phpstan-no-value-type-specified-in-iterable-type
  230    Function wp_localize_script() has parameter $l10n with no value type specified in iterable type array.
         🪪  missingType.iterableValue
         💡  See: https://phpstan.org/blog/solving-phpstan-no-value-type-specified-in-iterable-type
  366    Function wp_enqueue_script() has parameter $args with no value type specified in iterable type array.
         🪪  missingType.iterableValue
         💡  See: https://phpstan.org/blog/solving-phpstan-no-value-type-specified-in-iterable-type
 ------ --------------------------------------------------------------------------------------------------------

 ------ ------------------------------------------------------------------------------------------------------------------------------------
  Line   functions.wp-styles.php
 ------ ------------------------------------------------------------------------------------------------------------------------------------
  44     Function wp_print_styles() has parameter $handles with no value type specified in iterable type array.
         🪪  missingType.iterableValue
         💡  See: https://phpstan.org/blog/solving-phpstan-no-value-type-specified-in-iterable-type
  68     Parameter #1 $handles of method WP_Dependencies::do_items() expects array<string>|string|false, array|bool|non-empty-string given.
         🪪  argument.type
  101    Parameter #1 $string of function trim expects string, string|null given.
         🪪  argument.type
 ------ ------------------------------------------------------------------------------------------------------------------------------------

After:

[OK] No errors

Trac ticket: https://core.trac.wordpress.org/ticket/64238

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[westonruter]

Committed in r61402