fix: remove CSS @layer rule from static CSS bundle (#6430)

Author: Lukas742

config/merge-css-modules.js

@@ -20,7 +20,7 @@ for (const cssModule of cssModules) {
   const componentName = basename(cssModule, '.module.css');
 
   fileContent.push(`/* ${componentName} */`);
-  fileContent.push(cssContent);
+  fileContent.push(cssContent.replace('@layer ui5-webcomponents-react{', '').replace(/}$/, ''));
   fileContent.push('');
 }
 

config/postcss-config-factory.js

@@ -15,14 +15,6 @@ export function postcssConfigFactory(packageName) {
       cssLayersPlugin(),
       postcssModules({
         // generateScopedName: '[name]__[local]___[hash:base64:5]',
-        generateScopedName: function (name, filename, css) {
-          const file = path.basename(filename, '.module.css');
-          const i = css.indexOf(`.${name}`);
-          const lineNumber = css.substring(0, i).split(/[\r\n]/).length;
-          const hash = stringHash(css).toString(36).substring(0, 5);
-
-          return `${file}_${name}_${hash}_${lineNumber}`;
-        },
         getJSON: (cssFileName, json) => {
           return null;
         },

docs/knowledge-base/Styling.mdx

@@ -105,7 +105,8 @@ This would then be the result:
 
 ## Applying styling via `className` or `style`
 
-Almost all components allow setting `className` or `style` to style the component. For web components, this does **not** mean that styles are inherited by shadow root elements per default.
+Almost all components allow setting `className` or `style` for custom styling. For standard elements like `div`, `span`, etc., you can easily override internal CSS properties and values, as our styles are encapsulated in a [CSS layer](https://developer.mozilla.org/en-US/docs/Web/CSS/@layer).
+For web components, this does **not** mean that styles are inherited by shadow root elements per default.
 Only [inherited CSS properties](https://developer.mozilla.org/en-US/docs/Web/CSS/inheritance#inherited_properties) that are not set inside the shadow root or internally passed properties will change the styles of the internal elements.
 Another special case are abstract components like the `SuggestionItem`. The `ui5-suggestion-item` element is mainly there to pass props to the actual component inside the shadow root and is therefore not stylable.
 
@@ -114,6 +115,8 @@ Another special case are abstract components like the `SuggestionItem`. The `ui5
 By default, the `ThemeProvider` injects the CSS of the components during runtime. If you want to import the CSS bundles explicitly, you can set the `staticCssInjected` prop to `true`.
 This approach provides you with control over the order in which CSS files are injected, making it easier to override styles.
 
+Please note that the static CSS is not wrapped inside a [CSS layer](https://developer.mozilla.org/en-US/docs/Web/CSS/@layer). You can use the [`@import` CSS at-rule](https://developer.mozilla.org/en-US/docs/Web/CSS/@import) to achieve that.
+
 - **main** package import: `import '@ui5/webcomponents-react/styles.css'`
 - **charts** package import: `import '@ui5/webcomponents-react-charts/styles.css'`