Newlines in evaluated RegExp literals are not escaped

[RunDevelopment]

Bug report

When compression code of the form RegExp("any string literal"), new lines are not escaped resulting is syntactically incorrect code.

Version
uglify-js 3.6.0

Complete minify() options

{
	compress: {
		unsafe: true
	}
}

uglify-js input

console.log(RegExp("\\\nfo\n[\n]o\\bbb"));

uglify-js output

console.log(/\
fo
[
]o\bbb/);

Expected result

console.log(/\nfo\n[\n]o\bbb/);

---

Note: This is the same bug as this one.

[alexlamsl]

Very peculiar indeed - and since it's consistent across all Node.js versions (0.10 and above), I guess we'll need to work around this.

[RunDevelopment]

I actually wrote a fix for this for Terser. This is the main function.

Anyone feel free to make a PR/commit with the function in it.

[alexlamsl]

Thanks for the heads up - I've borrowed your test case in #3453