feat: middleware uses local resources when present

[vladitasev]

Short version:
This changes the way middleware handles thirdparty/ resource requests.

Long version:
Every resource that matches the reverseAliases was read from node_modules/ and transpiled. Basically, this means that any request for the web components libraries that has thirdparty/ is assumed to be found in node_modules/ as a dependency. While this is true for OpenUI5 itself (it has all @ui5/webcomponents* packages as devDependency), this is not the case for third-party libraries: for these, the OpenUI5 monorepo is not a dependency (only individual OpenUI5 libraries are), therefore third-party libraries do not have @ui5/webcomponents* as any kind of dependency. As a result, middleware requests to @ui5/webcomponents-icons and similar failed. This change fixes that by allowing the middleware to look for such files in the filesystem first. The third-party libraries will have @openui5/sap.ui.webc.common as a dependency and will be able to find the files in its src-gen directory as a result.