Move Chromium/WAM to the new agl-compositor

Closing the issue. We have created https://lf-automotivelinux.atlassian.net/browse/SPEC-3830#icft=SPEC-3830 to re-enable the browser app.

We are still looking into fixing the browser-service to be able to have chromium working with the new compositor. There were some dependencies with libwindowmanager removed, but we keep working on the pending removal of runxdg.

https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/25110  fixes the issue: going back to an app previously launched after switching to a different content.

We have kept working on this and made some changes to the homescreen:

• webapps-html5-homescreen is now a "panel left" surface showing the homescreen toolbar.

• We have added a new app, htm5-background which will be performing the "background" surface role: https://github.com/AGL-web-applications/background .  For the moment, we are pointing to this repository in meta-agl-demo, we can think later if it makes sense to add  a new gerrit repository for it.

We have started using this meta-layer while development is on-going: https://github.com/Igalia/meta-agl-html5-dev

Showing  HTML5 UI on boot  and launch webapps from the launcher works.

Homescreen side bar is hidden by the launcher and/or running webapps, we are working on a solution.