This MR forwards wlroots to 0.8.1 + cherry-picked important patches from current master (see the new librem5-0.8.x branch: https://source.puri.sm/Librem5/wlroots/tree/librem5-0.8.x).
One patch that is carried forward from 0.6.x branch is wlroots@749a2cdd, which is temporarily needed until phosh#157 (closed) is properly fixed.
This MR also contains the last patches that made it into rootston, but weren't included in phoc yet; it also reverts commit aec0a1ab which would need to be reworked to work with newer wlroots anyway (and phosh!261 (closed) that makes it obsolete is almost there).