For the fruit: Using a mortar and pestle, mini food processor or a sealed plastic bag and a mallet or rolling pin, crush the freeze-dried raspberries and strawberries together to a powder; some little pebbles are ok. Set aside 2 tablespoons for the icing and garnish.
For the dough: Spray the bottom and sides of an 8-inch square baking dish or 8- or 9-inch round pie pan with cooking spray.
Unroll the crescent dough out on a sheet of parchment paper. If using dough with perforations, gently pinch the seams to keep them together. Leaving about a 1-inch border on one of the short sides, sprinkle with the remaining fruit mixture, followed by a layer of the granulated sugar and then the brown sugar. Use a box grater or rasp and grate the butter evenly over the top. Starting with the short edge with the filling on it, roll, tucking as you go, towards the short edge with the empty border. Cut into 8 equal rounds and place in the prepared dish. Bake until the tops are golden, 13 to 14 minutes.
For the icing: While the danishes are baking, in a small bowl, whisk together the confectioners' sugar, 1 tablespoon of the reserved fruit mixture, a pinch of salt and 1 teaspoon of preferred liquid. The icing should be thick like a glaze, but thin enough to pour. If needed, add more liquid.
Drizzle the icing over the warm danishes. Transfer to plates and sprinkle with the remaining fruit mixture. Serve warm.