Fix for regression in zig fmt's handling of 'for-if'

[LewisGaul]

Fixes #8088

• Added testcase to reproduce the issue
• Factored out common code into renderWhilePayload()
• Determine whether newline is needed before the 'if'
• Fix indentation of the 'then' expression when no newline is inserted before the 'if'

[ifreund]

This is already an improvement over the status quo and fixes the regression. There's still some inconsistency here that I think would be good to iron out if you're game for it:

// zig fmt accepts this:
if (a)
    if (b)
        f(x);

// but changes this
if (a)
    for (b) |c|
        foo(x);
// to this:
if (a) for (b) |c|
    foo(x);

The same thing happens with while in the place of for

[LewisGaul]

This is already an improvement over the status quo and fixes the regression. There's still some inconsistency here that I think would be good to iron out if you're game for it:

Nice catch, I can certainly have a go at addressing that. Thanks again for taking a look.

[ifreund]

Thanks for getting the ball rolling on this! I took your work as a starting point and iterated a bit further to end in what I think is a much better place than the status quo :)