Revisit: Casing for tuple elements

[bkoelman]

Follow-up on #107 and #104 (comment), based on this article. After reading the article, I agree it would be better to distinguish between tuple element names and variables declared using tuple syntax.

So I propose to update the casing table in AV1702 like this:

1. Remove row "Tuple element"
2. Add row "Tuple element names"
   Casing: Pascal
   Examples:
   (string First, string Last) name = ("John", "Doe");
var name = (First: "John", Last: "Doe");
(string First, string Last) GetName() => ("John", "Doe");
3. Add row "Variables declared using tuple syntax":
   Casing: Camel
   Examples:
   (string first, string last) = ("John", "Doe");
var (first, last) = ("John", "Doe");