[clang-format] [PR43333] Fix C# breaking before function name when using Attributes

Summary:
This is  a fix for https://bugs.llvm.org/show_bug.cgi?id=43333

This comes with 3 main parts

  - C# attributes cause function names on a new line even when AlwaysBreakAfterReturnType is set to None
  - Add AlwaysBreakAfterReturnType  to None by default in the Microsoft style,
  - C# unit tests are not using Microsoft style (which we created to define the default C# style to match a vanilla C# project).

Reviewers: owenpan, klimek, russellmcc, mitchell-stellar

Reviewed By: mitchell-stellar

Subscribers: cfe-commits

Tags: #clang-tools-extra, #clang, #clang-format

Differential Revision: https://reviews.llvm.org/D67629

llvm-svn: 373707