[Issue 20007] Add the `__COUNTER__` special keyword

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20007

Basile-z <b2.temp at gmx.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Add a new expression        |Add  the `__COUNTER__`
                   |similar to the C            |special keyword
                   |`__COUNTER__` macro         |

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