docs(guides): Update asset-modules.mdx (#5289)

Fix dead links for the old loaders

Author: jmcscript

src/content/guides/asset-modules.mdx

@@ -16,9 +16,9 @@ Asset Modules is a type of module that allows one to use asset files (fonts, ico
 
 Prior to webpack 5 it was common to use:
 
-- [`raw-loader`](/loaders/raw-loader/) to import a file as a string
-- [`url-loader`](/loaders/url-loader/) to inline a file into the bundle as a data URI
-- [`file-loader`](/loaders/file-loader/) to emit a file into the output directory
+- [`raw-loader`](https://v4.webpack.js.org/loaders/raw-loader/) to import a file as a string
+- [`url-loader`](https://v4.webpack.js.org/loaders/url-loader/) to inline a file into the bundle as a data URI
+- [`file-loader`](https://v4.webpack.js.org/loaders/file-loader/) to emit a file into the output directory
 
 Asset Modules type replaces all of these loaders by adding 4 new module types: