clang-format: [JS] fix `??` opreator wrapping.

Summary:
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.

Reviewers: krasimir

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D73026