OS#14115684: Function-in-block semantics don't work for defer parse

[boingoing]

In below code repro, we do not create var decl binding for foo inside the nest function in defer-parse mode. Due to this, we leave the reference to foo in nest on the pid ref stack and bind it to the formal foo parameter from the test function. This leads us to think formal foo is captured and try to put it into a scope slot. However, formal foo is not actually captured so no scope slot is allocated. When we actually generate bytecode for test, we hit a fail fast.

function test(foo) {
    function nest() {
        {
            function foo() {
                console.log('pass');
            }
        }
        foo();
    }
    nest();
}
test(()=>console.log('fail'));

Fix is to create the var binding for foo at the function declaration for foo even in defer-parse mode.

Fixes:
https://microsoft.visualstudio.com/web/wi.aspx?id=14115684

[boingoing]

@dotnet-bot test OSX static_osx_osx_debug please

[boingoing]

Thanks, Paul.