clang-format: [JS] do not collapse - - to --.
However the two tokens must not collapse together: --1 is prefix
decrement, i.e. different syntax.
- -1; ==> --1;
- -1; ==> - -1;
This change makes no attempt to format this "nicely", given by all
likelihood this represents a programming mistake by the user, or odd
The check is not guarded by language: this appears to be a problem in
Java as well, and will also be beneficial when formatting syntactically
incorrect C++ (e.g. during editing).
Differential Revision: https://reviews.llvm.org/D99495