Allow for custom ModuleScopePlugin error messaging

[Aghassi]

create-react-app/packages/react-dev-utils/ModuleScopePlugin.js

Lines 15 to 19 in a422bf2

	constructor(appSrc, allowedFiles = []) {
	this.appSrcs = Array.isArray(appSrc) ? appSrc : [appSrc];
	this.allowedFiles = new Set(allowedFiles);
	this.allowedPaths = [...allowedFiles].map(path.dirname).filter(p => path.relative(p, process.cwd()) !== '');
	}

I like using this plugin directly when I write my own webpack configs, and I think it would be beneficial to allow developers to pass a custom error message to the constructor that takes precedence over the default message. It would not be a breaking change, but would be a welcomed one so I don't have to patch in my own logic. I'm also happy to issue a PR for this if the maintainers are interested in allowing this to happen.

My specific use case is I'm working with Webpack under Bazel (bazel.build) and would like to provide more explicit error handling since the failure cases are more nuanced.

I've created #11978 as a PoC