Arguably terrible enum identifiers causes breakage.

[oBusk]

So I was trying to run knip on a larger project and was runing into errors that was not very clear to me at first.

file:///Z:/My_Large_Repo/node_modules/knip/dist/typescript/getImportsAndExports.js:298
        for (const match of sourceFile.text.matchAll(new RegExp(item.identifier.replace(/\$/g, '\\$'), 'g'))) {
                                                     ^

SyntaxError: Invalid regular expression: /+/g: Nothing to repeat
    at new RegExp (<anonymous>)
    at setRefs (file:///Z:/My_Large_Repo/node_modules/knip/dist/typescript/getImportsAndExports.js:298:54)     
    at getImportsAndExports (file:///Z:/My_Large_Repo/node_modules/knip/dist/typescript/getImportsAndExports.js:314:13)
    at ProjectPrincipal.analyzeSourceFile (file:///Z:/My_Large_Repo/node_modules/knip/dist/ProjectPrincipal.js:140:47)
    at analyzeSourceFile (file:///Z:/My_Large_Repo/node_modules/knip/dist/index.js:187:66)
    at main (file:///Z:/My_Large_Repo/node_modules/knip/dist/index.js:268:17)
    at async run (file:///Z:/My_Large_Repo/node_modules/knip/dist/cli.js:25:73)
    at async file:///Z:/My_Large_Repo/node_modules/knip/dist/cli.js:85:1

After adding some logging into the getImportsAndExports.js I managed to find that it was choking parsing an enum we have to handle potential values of KeyboardEvent.key, including keys like * and +, which is arguably a terrible idea, but is allowed in Typescript, so I guess knip shouldn't fail on it either.

Here's a repro: https://stackblitz.com/edit/github-4tmeki?file=enum.ts%3AL21

I think it should be pretty easy to amend, I might send a PR too

[webpro]

Knip should definitely not choke on those indeed. A PR would be great, otherwise I'll pick it up after the weekend.