[clang-format] Handle commas in [] in C#

Summary:
Respect setting `SpacesInSquareBrackets` for commas in square brackets in C# code.

Reviewers: krasimir, MyDeveloperDay

Reviewed By: krasimir

Subscribers: cfe-commits

Tags: #clang-format, #clang

Differential Revision: https://reviews.llvm.org/D75182