Honor compilation target when checking JavaScript

[jrieken]

There is a code branch for JavaScript specific checks but it doesn't honour the target defined in the compiler options. When ES3 or ES5 is being used these things should be reported as errors as well

• use of arrow function
• use of const and let
• use of default parameter values
• short hand object literal notation
• ...

Also, I wonder if this code path can be executed in addition to the semantic analysis instead of instead.

[mhegazy]

I think target is the wrong property here. we need something else to mean sourceVersion or something along these lines.

[sheetalkamat]

With #5471 we would be emit the es3 and es5 syntax of javascript input file for es6 syntax hence these are not errors any more