asm grammar dosn't covers bracket syntax

[dlangBugzillaToGithub]

Mai Lapyst reported this on 2024-05-07T18:59:09Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=24544

Description

The current grammar for asm statements does not cover the following code:

```d
asm {
  mov ECX, [ESP + 1]
}
```

While there exists a rule in `AsmBrExp` that allows for some brackets, they require an expression before the beginning bracket:

```d
void* pc;
asm {
  mov  pc[EBP],EBX
}
```