Change "Whitepoint" label to "White"

This addresses confusion with those already familiar with the term "white point" which is often used to describe something different than the white parameter of tonemapping function: godotengine/godot#87260 (comment)

Author: allenwp

3d/tonemap_color_correction/test.tscn

@@ -89,7 +89,7 @@ theme_override_constants/separation = 10
 [node name="Label" type="Label" parent="Options/TonemapMode/Whitepoint"]
 layout_mode = 2
 size_flags_horizontal = 3
-text = "Whitepoint"
+text = "White"
 horizontal_alignment = 2
 
 [node name="HSlider" type="HSlider" parent="Options/TonemapMode/Whitepoint"]