[9.x] Backed enum support for @js

[nuernbergerA]

Current state of enum in @js

Given we have an defined enum:

enum Thing: string
{
    case SIMPLE = 'simple';
    //...
}

and pass it into @js

@js(Thing::SIMPLE)

Will output:

JSON.parse('\u0022simple\u0022')

After this PR

'simple'