Bytes: Fix length from fromBytes on JS

[Geokureli]

Potentially related to: openfl/openfl#2360

In JS the underlying byte data may have extras, due to the underlying types used in js, explained here: HaxeFoundation/haxe#8974. This pr will ignore those extras.

Example reproducing the inconsistent behavior:

final output = new haxe.io.BytesOutput();
output.writeString("test");
final byteArray = lime.utils.Bytes.fromBytes(output.getBytes());
trace('byteArray.length: ${byteArray.length}'); // 16 on JS, 4 otherwise

Tested on chrome for mac

[player-03]

Tested on chrome for mac

I also got 16 in Firefox on Linux.

[Geokureli]

I also added a fix to haxe, but lime should probably account for this on older versions

[tobil4sk]

slice copies the buffer, so perhaps another option might be to just manually override: this.length = length? (might require @:privateAccess)

[Geokureli]

doesn't require @:privateAccess as the abstract has @:access(haxe.io.Bytes)