Fix Curve point properties usage flags

[kleonc]

Fixes #116323.
Fixes #116442

Regression from #92282:

Curve/Curve2D/Curve3D per point properties were incorrectly changed to use default usage flags (including PROPERTY_USAGE_STORAGE). These should be editor-only, actual data is stored in a single _data property per curve.
Duplicated data in #116323 MRP:

[sub_resource type="Curve" id="Curve_tgo4v"]
resource_local_to_scene = true
_limits = [1.0, 8.0, 0.0, 1.0]
_data = [Vector2(0, 1.103612), 0.0, 0.0, 0, 0, Vector2(1, 8), 0.0, 0.0, 0, 0]
point_count = 2
point_0/position = Vector2(0, 1.103612)
point_1/position = Vector2(1, 8)

---

Curve::_set_point_position got value/offset values swapped. But in fact, before #92282 there was a bug in the Curve::_set, as when setting a point position it was setting the offset before the value for the same point index:

godot/scene/resources/curve.cpp

Lines 585 to 588 in f346633

	if (property == "position") {
	Vector2 position = p_value.operator Vector2();
	set_point_offset(point_index, position.x);
	set_point_value(point_index, position.y);

but setting the offset for a point at given index might result in changing the index of the given point (as points are sorted by offsets). Correct is either:

set_point_value(point_index, position.y);
set_point_offset(point_index, position.x);

or:

int new_index = set_point_offset(point_index, position.x);
set_point_value(new_index, position.y);

[shakesoda]

thanks, curve edit is totally unusable without this rn

[Repiteo]

Thanks!