Raw bracket is not allowed in regular expression with unicode flag

Hello,
This regexp is not valid, but chakra pass without throw a syntax error.

version: 1.11.19
OS: Linux Ubuntu 19.10 x64

steps to reproduce:
```
var x = /[\u{61}-b]b]/u;
^
```
Actual results:
```
pass without errors
```

Expected results:
```
SyntaxError: raw bracket is not allowed in regular expression with unicode flag
```
V8, SpiderMonkey, Hermes and JavaScriptCore works as expected.

cinfuzz