Render contextual links taking the current page theme into account

Problem/Motivation

If the default theme is doing theming customisations on the contextual links, the contextual links in the admin theme may be broken.

Because currently contextual links are constantly rendered with the default theme and not the current page theme.

I witnessed broken contextual links with the UI Suite Bootstrap theme with changes from 🐛 Access to footer settings Active (which I will revert until a solution will be found).

Steps to reproduce

Change the display of contextual links on the default theme and see the impact on the admin theme.

Proposed resolution

Contextualize the rendering of the contextual links with the current page theme.

Remaining tasks

API changes