Add dynamic return type extension for `wp_tag_cloud()`

[IanDelMar]

This PR adds a dynamic function return type extension for wp_tag_cloud().

I have made several updates to the extension since the initial draft:

• It now only checks for an array parameter or an empty string.
• The use of instanceof has been removed.
• It requires version 5.8.4+ of wordpress-stubs.

[IanDelMar]

I'll have a look at the failed checks tomorrow.

[herndlm]

Jfyi I think we need to be careful to not introduce too many instanceof checks, see also https://phpstan.org/blog/why-is-instanceof-type-wrong-and-getting-deprecated :)

But don't let this block you here, maybe for the next PR. We can try to refactor some away later

[IanDelMar]

@herndlm Thank you! I wasn't aware of that.

[IanDelMar]

Implemented in stubs https://github.com/szepeviktor/phpstan-wordpress/pull/147