First Draft: ref For Variable Declarations

[Nick Treleaven]

On Friday, 12 April 2024 at 20:43:50 UTC, Walter Bright wrote:
> https://github.com/WalterBright/documents/blob/984374ca885e1cb10c2667cf872aebc13b4c1663/varRef.md

Ref variables would be useful for refactoring. E.g. to disallow 
foreach over an array with a non-const `ref` index - related to:
https://issues.dlang.org/show_bug.cgi?id=24499

```d
foreach (ref i, ref e; array) {
     // code that modifies `i`, causing skipped/repeated elements 
of foreach
```
Rewrite to:
```d
for (size_t i; i < array.length; i++) {
     ref e = array[i];
     // code that modifies `i`, which is now less surprising
```

Currently you'd have to write `ref e() => array[i];`, which is 
less intuitive and is not the same if `array` is reassigned 
between calls to `e`.