refactor: fix modernize-return-braced-init-list warnings (#44838)

* refactor: avoid repeating the return type from the declaration; use a braced initializer list instead [modernize-return-braced-init-list]

* refactor: avoid repeating the return type from the declaration; use a braced initializer list instead [modernize-return-braced-init-list]

NB: using the braced-initializer list uncovered an error here:
the float returned by std::floor() can't be implicitly cast to
an int. This is solved by using base::ClampFloor<int>() instead.
std::floor()

shell/browser/api/electron_api_screen.cc

@@ -82,7 +82,7 @@ gfx::Point Screen::GetCursorScreenPoint(v8::Isolate* isolate) {
     thrower.ThrowError(
         "screen.getCursorScreenPoint() cannot be called before a window has "
         "been created.");
-    return gfx::Point();
+    return {};
   }
 #endif
   return screen_->GetCursorScreenPoint();