Fix window maximization when using splash screen

Avoid eager restore of maximized state in `TheiaElectronWindow.init`
when a splash screen is configured (i.e. `preventAutomaticShow` config
option is false)
Calling `window.maximize()` implicity also makes the window visibile.
If `preventAutomaticShow` is true we have to make sure to invoke
`restoreMaximizeState` after the main window is ready.
Otherwise both the splashscreen and the preload window will be visible
at the same time

Fixes eclipse-theia#14218

packages/core/src/electron-main/theia-electron-window.ts

@@ -85,8 +85,8 @@ export class TheiaElectronWindow {
         this._window.setMenuBarVisibility(false);
         if (!this.options.preventAutomaticShow) {
             this.attachReadyToShow();
+            this.restoreMaximizedState();
         }
-        this.restoreMaximizedState();
         this.attachCloseListeners();
         this.trackApplicationState();
         this.attachReloadListener();
@@ -196,6 +196,9 @@ export class TheiaElectronWindow {
     protected trackApplicationState(): void {
         this.toDispose.push(TheiaRendererAPI.onApplicationStateChanged(this.window.webContents, state => {
             this.applicationState = state;
+            if (state === 'ready' && this.options.preventAutomaticShow) {
+                this.restoreMaximizedState();
+            }
         }));
     }