[clang-format]: Add NonEmptyParentheses spacing option

This patch aims to add support for the following rules from the JUCE coding standards:

- Always put a space before an open parenthesis that contains text - e.g. foo (123);
- Never put a space before an empty pair of open/close parenthesis - e.g. foo();

Patch by Reuben Thomas

Differential Revision: https://reviews.llvm.org/D55170

llvm-svn: 357344