UDAs with single template argument are sandwiched with declaration

Input:
```D
@1 float f() => 1.0;

@"test name" unittest 
{
}
```

Expected output: the same
Actual dfmt output:

```D
@1float f() => 1.0;

@"test name"unittest
{
}
```

The spaces after the attributes are removed, leading to code that looks worse or won't even compile anymore if you're unlucky.

