port shell-js to c++

https://bugzilla.gnome.org/show_bug.cgi?id=711052
remove direct access to jsapi

with js24 its not possible to access jsapi directly from C code

https://bugzilla.gnome.org/show_bug.cgi?id=711052
lookingGlass: Remove Memory tab and add a gc Icon to toolbar

With js24 it won't be possible to access gjs memory stats from C code.

https://bugzilla.gnome.org/show_bug.cgi?id=711052