Add EditContext.IsValid(..) to determine if a field has any associated validation messages.

Background and Motivation

Add an API to query if a FieldIdentifier is valid without having to get validation messages. We have several places that get the messages only to determine this condition e.g. https://github.com/dotnet/aspnetcore/blob/main/src/Components/Web/src/Forms/InputBase.cs#L245

This has the sneaky benefit of removing yet another Linq call because we do something more optimized to determine this condition.

// some lines of code here
var isValid = EditContext.IsValid(FieldIdentifier);
if (!isValid)
{
   // Do stuff
}

@pranavkm

@pranavkm is this something you envision for 7.0?

This would be a great enhancement!