Well this is not straight forward but from what I can think here is , you need to start writing your own custom module to do the validation.
first of all use regex to differentiate between folder, url, and file value.
once identified folder and files are easy to detect with Directory and File .Exist
for url use the web connect method, get the status code and confirm that urls is accessible. make sure you use try catch , all 500 will raise exception.
once done you can write plugin to build msbuild custom action or run via jenkins.