Because we should improve code format style.

I know there are some opposite opinions about template constraint indentation style.
But from my experience, I think this is *practically* better.

If template constraint is very long, one level indentation will decrease column count that would be able to use for actual code formatting.

For example, let's see `std.algorithm.sort`:

```d
SortedRange!(Range, less)
sort(alias less = "a < b", SwapStrategy ss = SwapStrategy.unstable,
        Range)(Range r)
    if (((ss == SwapStrategy.unstable && (hasSwappableElements!Range ||
                                          hasAssignableElements!Range)) ||
         (ss != SwapStrategy.unstable && hasAssignableElements!Range)) &&
        isRandomAccessRange!Range &&
        hasSlicing!Range &&
        hasLength!Range)
```

VS:

```d
SortedRange!(Range, less)
sort(alias less = "a < b", SwapStrategy ss = SwapStrategy.unstable,
        Range)(Range r)
if (((ss == SwapStrategy.unstable && (hasSwappableElements!Range ||
                                      hasAssignableElements!Range)) ||
     (ss != SwapStrategy.unstable && hasAssignableElements!Range)) &&
    isRandomAccessRange!Range &&
    hasSlicing!Range &&
    hasLength!Range)
```

If the column limit is 80:
- With first style, you can use 80-8 columns for the constraint expression formatting.
- With second style, you can use 80-4 columns for the constraint expression formatting.

This 4-column difference is not small, when considering word wrapping.

---

Btw, I'm separating commits based on the changing purpose.
You can see diffs on each commits. There's no clogging.