clang-format: [JS] do not insert whitespace in call positions.

Summary:
In JavaScript, may keywords can be used in method names and thus call sites:

    foo.delete();
    foo.instanceof();

clang-format would previously insert whitespace after the `instanceof`. This
change generically skips inserting whitespace between a keyword and a
parenthesis if preceded by a dot, i.e. in a callsite.

Reviewers: djasper

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D36142

llvm-svn: 310851