[Update existing sniff] Allow register_block_style

[carolinan]

In https://github.com/WPTRT/WPThemeReview/blob/develop/WPThemeReview/Sniffs/PluginTerritory/ForbiddenFunctionsSniff.php
The sniff for regestering blocks is too strict.

The existing sniff is for 'register_block_*', so an error is shown for register_block_style().
register_block_style() is allowed in themes, so it should not cause an error.

To do:

• Add the rule in the Theme Review handbook to the Requirements page.
• Add the rule in the Theme Review handbook to the Recommended page.
• Move the rule in the Theme Review handbook to the Requirements page.
• Create unit tests
• Create new sniff
• Adjust existing WPCS / PHPCS sniff and send in PR upstream.
• Add existing sniffname sniff to the ruleset.

[dingo-d]

A PR for this is straightforward:

Check https://developer.wordpress.org/?s=register_block_&post_type%5B%5D=wp-parser-function for all the register_block_* type functions, add them manually but exclude the style one.

Thanks for noticing this 👍