Stop using the enum as a manifest constant.

[Jack Applegame]

On Sunday, 6 June 2021 at 10:24:54 UTC, evilrat wrote:
> Nah, that enum arrays specifically,

Except for character arrays. Just change `int[]` to 
`char[]`/`wchar[]`/`dchar[]`.

```asm
void example.useEnum():
         push    rbx
         lea     rbx, [rip + .L.str]
         mov     edi, 3
         mov     rsi, rbx
         call    @nogc void example.sideEffect(const(char[]))@PLT
         mov     edi, 3
         mov     rsi, rbx
         pop     rbx
         jmp     @nogc void example.sideEffect(const(char[]))@PLT

void example.useConst():
         push    rbx
         lea     rbx, [rip + .L.str]
         mov     edi, 3
         mov     rsi, rbx
         call    @nogc void example.sideEffect(const(char[]))@PLT
         mov     edi, 3
         mov     rsi, rbx
         pop     rbx
         jmp     @nogc void example.sideEffect(const(char[]))@PLT
```

> deprecating this specific case is probably ok though.

That's not enough. Let's deprecate any use of enum as a manifest 
constant.