Customize: Define params on `WP_Customize_Partial::render_callback()` for the...

Customize: Define params on `WP_Customize_Partial::render_callback()` for the sake of subclasses overriding this method.

Fixes a strict standards notice regarding the method signature needing to be compatible.

See #27355.

Built from https://develop.svn.wordpress.org/trunk@36801


git-svn-id: https://core.svn.wordpress.org/trunk@36768 1a063a9b-81f0-0310-95a4-ce76da25c4cd