braceless with statements

[Dennis]

On Friday, 12 November 2021 at 10:55:21 UTC, Stefan Koch wrote:
> It is a really simple patch and I think it's worthwhile to have 
> this in the main language.

How about other statements, like `if`, `for`, `foreach`, 
`switch`? When extending `attribute:` syntax to statements, might 
as well include all of them for consistency. N.b. this is already 
allowed in global scope:
```D
static if (true):
```
Not in function scope though.