Make ANIMATION_CALLBACK_MODE_DISCRETE_DOMINANT be default for AnimationPlayer

[TokageItLab]

Follow up #86629.

ANIMATION_CALLBACK_MODE_DISCRETE_RECESSIVE performs no conversion to Continuous and applies the AnimationMixer blend. This was a problem in AnimationPlayer as discussed in #80813 (comment), so we make ANIMATION_CALLBACK_MODE_DISCRETE_FORCE_CONTINUOUS the default in 4.2.

In other words, ANIMATION_CALLBACK_MODE_DISCRETE_RECESSIVE was the default in the old AnimationPlayer that caused problems during AnimationMixer development. So in 4.3, ANIMATION_CALLBACK_MODE_DISCRETE_DOMINANT should be the default for the AnimationPlayer.

[CookieBadger]

I just came across these changes. Does this PR fix this issue?

The offending function:

Animation::UpdateMode Animation::value_track_get_update_mode(int p_track) const {
	ERR_FAIL_INDEX_V(p_track, tracks.size(), UPDATE_CONTINUOUS);
	Track *t = tracks[p_track];
	ERR_FAIL_COND_V(t->type != TYPE_VALUE, UPDATE_CONTINUOUS);

	ValueTrack *vt = static_cast<ValueTrack *>(t);
	return vt->update_mode;
}

Called from animation_mixer.cpp::1422, when the type is Bezier (reproducing error probably requires a Bezier track)

...
case Animation::TYPE_BEZIER:
case Animation::TYPE_VALUE: {
	if (Math::is_zero_approx(blend)) {
		continue; // Nothing to blend.
	}
	TrackCacheValue *t = static_cast<TrackCacheValue *>(track);
	bool is_discrete = a->value_track_get_update_mode(i) == Animation::UPDATE_DISCRETE;
	...

[TokageItLab]

@CookieBadger It is not related with this PR, but fixed by #88488

[Mickeon]

Docs are fine but that of course is not the most important part right now.

[akien-mga]

Thanks!