Single line conditions

When using simple conditions for early returns / guard statements the current formatting is quite verbose:

function test($arg1) {
  if (!$arg) return;

  for ($i = 0; $i < 10; $i++) {
    if ($i % 2 === 0) continue;
    // do something if the number is odd
  }
}

will be converted to:

function test($arg1) {
  if (!$arg) {
    return;
  }

  for ($i = 0; $i < 10; $i++) {
    if ($i % 2 === 0) {
      continue;
    }
    // do something if the number is odd
  }
}

It would be great if these single line conditions would be preserved. Alot of formatters for c-style languages like prettier for javascript or ClangFormat allow this, resulting in much more concise code.

Start with the PHP examples in the issue and inspect the formatter's handling of single-line early returns, guard statements, and loop controls. Determine how the current block expansion is implemented and identify the relevant existing tests before defining the expected preserved formatting. Done means these single-line conditions remain concise while other formatting behavior is unchanged.