meson: Enabling mutter hybrid graphics gles3 support is controlled by same option as cogl-gles2 build
In autotools, the backends/meta-gles3*
stuff was always built, regardless of the cogl-gles2 choice, and it seems to have worked fine (at least until not exercising that code path with actual hybrid graphics hardware). Though on my end I patched it to be dependent on native backend being enabled, as it seemed mainly used there and otherwise introduced a gles2 dep even for builds having wayland/native_backend disabled.
But now with meson, -Dgles2 controls both mutters gles3 usage and the build of cogl-gles2. I'm not sure if cogl-gles2 is ever used - perhaps useful for embedded platforms only, if even that. Unless I'm misguided, could we have separate options to control this, as to not end up with mutter-cogl-gles2 that doesn't get used?