@section should not be legal in .razor files

[chsienki]

The @section directive should only apply to MVC and razor pages: https://learn.microsoft.com/en-us/aspnet/core/mvc/views/razor?view=aspnetcore-9.0#section

Today, it's legal to add a @section to a .razor file, but the generated code causes errors.
https://lab.razor.fyi/#lZBBSkNBDIYp3c3ChV4gvJWCjAewlpaC2EK7aEUXpch0XtoO-CZDkidY6cqdB_AAXsOFR_IKoq_tSuG5S_58Sf7EvDXM0TWK9qhIFDGqZbcmPnxpdBbE6PwKjh8cg6DXQBFChEkVyol5MgAArdTeStDZYq2z1DYbY3Y5dOe-gn9UTzlWqSiHuJzO9kPhAqaZm_vsFLIcF9ns3GzMa9Mc3PWLRKyy9ffc_Hz_6JQS4hImj6JY2BGqvVJN5nfZDoTirjYMnkloobYraYTaI0a7_4HYbqkr4rB236bqNl0SF1IXHlOpIS7r4rc436GiToOv02HHGHPkIeX4jz32JrCW7v7P6weTflRkSl8

We should not allow @sections in .razor files.

[jjonescz]

Someone could depend on the codegen by inheriting their components from some custom class that has a DefineSection method. I imagine it would be possible to have a useful working @section system in .razor pages with that. RazorLab