Docs: Clarify documentation for `WP_Role::has_cap()` to more clearing indicate...

Docs: Clarify documentation for `WP_Role::has_cap()` to more clearing indicate that the method checks for capabilities against the role rather than the user.

Also updates syntax in the DocBlock summary and description.

Props GunGeekATX for the initial patch.
Fixes #35080.

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git-svn-id: https://core.svn.wordpress.org/trunk@35899 1a063a9b-81f0-0310-95a4-ce76da25c4cd