Add screenshot to save file

[BarthPaleologue]

When saving the game (in cosmosJourneyer.ts in generateSaveData), create a small screenshot of the game and save it to the save file as a base64 string.

Resource: https://forum.babylonjs.com/t/how-should-i-use-screenshottools-create-screenshot-with-resize-async/55363/2

Then change the loading save panel ui to display the screenshot.

[BarthPaleologue]

How to do it:

• In SaveFileData

  CosmosJourneyer/src/ts/saveFile/saveFileData.ts

  Line 12 in 58901f3

  export type SaveFileData = {

  add a thumbnail stringfield.

• CosmosJourneyer::generateSaveData, call Tools.CreateScreenshotAsync to the base 64 string for the thumbnail (use a small size parameter, we don't want a 4k image data in the save file)

• In SaveLoadingPanelContent::createSaveDiv, add an image to display the thumbnail save between the save info on the left and the control buttons on the right.