fix: window maximization when using splash screen (#14219)

Avoids eager restore of maximized state in TheiaElectronWindow.

Calling `window.maximize()` implicitly also makes the window visible.
Therefore we have to check if the window is already visible before
restoring the maximizeState. If the window is not yet visible yet we
restore the state once the window is shown.

Fixes #14218

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

@@ -186,10 +186,18 @@ export class TheiaElectronWindow {
     }
 
     protected restoreMaximizedState(): void {
-        if (this.options.isMaximized) {
-            this._window.maximize();
+        const restore = () => {
+            if (this.options.isMaximized) {
+                this._window.maximize();
+            } else {
+                this._window.unmaximize();
+            }
+        };
+
+        if (this._window.isVisible()) {
+            restore();
         } else {
-            this._window.unmaximize();
+            this._window.once('show', () => restore());
         }
     }