Check if DisplayServer supports icons before attempting setting it

[akien-mga]

Silences this error when editing or running any project with Wayland:

WARNING: Icon not supported by this display server.
     at: set_icon (servers/display_server.cpp:591)

Inspired by #89099 and #89178.

@bruvzg We should likely apply the same treatment to all feature-specific APIs so we only call them internally when they're supported. I applied it to set_native_icon here while I was at it.

[bruvzg]

FEATURE_NATIVE_ICON checks are pretty redundant, all are in platform specific #ifdefs, but I guess it's OK for readability.

Other platform specific features should already have feature checks (at least menu and macOS expand to title bar, not sure if there are other). I guess it's it was missing for FEATURE_ICON since it was supported by all platforms before Wayland addition.

[Riteo]

Looks perfect!

[Riteo]

FEATURE_NATIVE_ICON checks are pretty redundant, all are in platform specific #ifdefs, but I guess it's OK for readability.

Yeah we should kinda make the whole warning logic more consistent. Perhaps emit a warning for all optional features, giving the caller the responsibility of calling it and gracefully fallbacking (if possible) when needed.