keep DataView only if we use Float32Array or Float64Array (see #4259)

std/js/html/compat/DataView.hx

@@ -22,7 +22,7 @@
 package js.html.compat;
 import haxe.io.Error;
 
-@:keep
+@:ifFeature("haxe.io.Float32Array.*", "haxe.io.Float64Array.*")
 @:access(js.html.compat.ArrayBuffer)
 class DataView {