Fix slint warnings in the docs

api/cpp/docs/generated_code.md

@@ -45,7 +45,7 @@ by a `std::vector<T>`.
 Let's assume we've this code in our `.slint` file:
 
 ```slint,no-preview
-component SampleComponent inherits Window {
+export component SampleComponent inherits Window {
     in-out property<int> counter;
     in-out property<string> user_name;
     callback hello;

docs/reference/src/language/concepts/layouting.md

@@ -96,7 +96,7 @@ A special case is to set the preferred size to be the size of the parent using `
 For example,this component will use the size of the parent by default:
 
 ```slint
-component MyComponent {
+export component MyComponent {
     preferred-width: 100%;
     preferred-height: 100%;
     // ...