clang-format currently treats the nullish coalescing operator ?? like
the ternary operator. That causes multiple nullish terms to be each
indented relative to the last ??, as they would in a ternary.
The ?? operator is often used in chains though, and as such more
similar to other binary operators, such as ||. So to fix the indent,
set its token type to ||, so it inherits the same treatment.
This opens up the question of operator precedence. However, ?? is
required to be parenthesized when mixed with || and &&, so this is
not a problem that can come up in syntactically legal code.