[cs] Generated casts are not consistent sometimes

[RealyUniqueName]

import cs.NativeArray;

class Main {
	public static function main() {
		var a:Arr<String> = Arr.alloc(10);
		var a2 = a.map(function(v) return Std.parseInt(v));
	}
}

class Arr<T> {
	public var length(default, null):Int;

	var __a:NativeArray<T>;

	public inline static function alloc<Y>(size:Int):Arr<Y> {
		return new Arr(new NativeArray(size));
	}

	function new(native:NativeArray<T>) {
		this.length = native.Length;
		this.__a = native;
	}

	public inline function map<S>(f:T->S):Arr<S> {
		var ret = alloc(length);
		for (i in 0...length)
			ret.__unsafe_set(i, f(__unsafe_get(i)));
		return ret;
	}

	inline function __unsafe_get(idx:Int):T {
		return __a[idx];
	}

	inline function __unsafe_set(idx:Int, val:T):T {
		return __a[idx] = val;
	}
}

$ haxe -main Main -cs bin
haxelib run hxcs hxcs_build.txt --haxe-version 4000 --feature-level 1
Note: dmcs is deprecated, please use mcs instead!
src/Main.cs(38,44): error CS0030: Cannot convert type `object[]' to `haxe.lang.Null<int>[]'
Compilation failed: 1 error(s), 0 warnings

Generated code for main function:

public static void main() {
  global::Array<string> a = new global::Array<string>(new string[]{"1", "2"});
  // vvv Here everything is object[] vvv
  global::Array<object> ret = new global::Array<object>(((object[]) (new object[a.length]) ));   {
    int _g = 0;
    int _g1 = a.length;
    while (( _g < _g1 )) {
      int i = _g++;
      {
        global::haxe.lang.Null<int> val = global::Std.parseInt(((string) (a.__a[i]) ));
        // vvv Here it's Nill<int>[] (this is line 38) vvv
        ((global::haxe.lang.Null<int>[]) (ret.__a) )[i] = val; 
      }

    }

  }

  global::Array<object> a2 = ret;
}

Both emphasized lines have the same types in AST. But generated types in cs are different.

[RealyUniqueName]

Was blocking #5749