fix(2356): omit numeric separators when targeting es2020

[a-tarasyuk]

Fixes #2356

[jakebailey]

Took me a bit to figure out what the Strada code did but, yeah:

        const flags = (neverAsciiEscape ? GetLiteralTextFlags.NeverAsciiEscape : 0)
            | (jsxAttributeEscape ? GetLiteralTextFlags.JsxAttributeEscape : 0)
            | (printerOptions.terminateUnterminatedLiterals ? GetLiteralTextFlags.TerminateUnterminatedLiterals : 0)
            | (printerOptions.target && printerOptions.target >= ScriptTarget.ES2021 ? GetLiteralTextFlags.AllowNumericSeparator : 0);

        return getLiteralText(node, sourceFile, flags);

Unbelievably, this is the only reason we pass the target into the printer.

(I do bet we have other things that are missing, though.)

[jakebailey]

Er, actually, no, getLiteralTextOfNode is where this should live, which is where I pulled the above code from. There is a TODO there for this (and related code).