Control flow directives (@if, @foreach) allowed inside @code block

Razor currently allows Razor control flow directives like ` @if ` and `@foreach` inside the `@code` block of a component.

This behaviour should probably be either be disallowed, or produce a dianostic warning/error because it blurs the distinction between Razor syntax and C#.

The issue names no files, tests, or entry points. Start by reproducing the behavior in a Razor component and determine whether the intended resolution is to reject the directives or emit a diagnostic; done requires that behavior and its expected diagnostic or error be specified and covered by tests.

Written by the indexing model from the issue text.