TypeScript: Support numeric separators

Created by: ulrichb

Describe the bug

Numeric separators (e.g. 10_000_000) are supported in TypeScript since version 2.7. It's still an ES (stage 3) proposal, therefore it doesn't get transpiled by Babel. So you get errors like the following.

./src/FrontEnd/App.tsx
SyntaxError: ....\App.tsx: Identifier directly after number (17:14)

  15 | import { reduxStore } from "./ReduxStore";
  16 | 
> 17 | console.log(10_000_000);

Steps to reproduce

See above.

Expected behavior

No transpile error.

Actual behavior

See above.

Reproducible demo

In any .ts/.tsx file:

console.log(10_000_000);

Solution

Add the "@babel/plugin-proposal-numeric-separator" plugin to the Babel preset if TypeScript is enabled. (Just like we do it for decorators.)