Fix #2423: Add CSP NONCE to inline style elements if found

[melloware]

###Defect Fixes
Fix #2423: Add CSP NONCE to inline style elements if found

This is a very important fix for security. This checks if the downstream application using PrimeReact has set a CSP NONCE environment variable process.env.REACT_APP_CSS_NONCE. This can be hardcoded in their .env file or if they are using a dynamic NONCE generator like CRA CSP WebPack Plugin: https://github.com/slackhq/csp-html-webpack-plugin.

If you do dynamically generate your NONCE you can easily set it in your application like this for PrimeReact to pick it up and use it in all its inline styling efforts.

// attempt to read an existing NONCE from a  CSS link on the page
let nonce;
let cssLink = document.querySelector('link[nonce]') as HTMLScriptElement;
if (cssLink) {
    nonce = cssLink?.nonce!;
}

// now set the environment variable for PrimeReact to read
if (nonce) {
    process.env.REACT_APP_CSS_NONCE= nonce;
}

[mertsincan]

Thanks a lot!