Support window blur in addition to transparency (#161)

Adds support for window blur via the Vibrancy feature on macOS and the
BackgroundMaterial feature on Windows. The setting has no effect on
Linux. If both transparency and blur are set, transparency will take
precedence.

emain/emain.ts

@@ -324,8 +324,20 @@ function createBrowserWindow(
         autoHideMenuBar: true,
     };
     const isTransparent = settings?.window?.transparent ?? false;
+    const isBlur = !isTransparent && (settings?.window?.blur ?? false);
     if (isTransparent) {
         winOpts.transparent = true;
+    } else if (isBlur) {
+        switch (unamePlatform) {
+            case "win32": {
+                winOpts.backgroundMaterial = "acrylic";
+                break;
+            }
+            case "darwin": {
+                winOpts.vibrancy = "fullscreen-ui";
+                break;
+            }
+        }
     } else {
         winOpts.backgroundColor = "#222222";
     }