[clang-format] [PR43100] clang-format C# support does not add a space between "using" and paren

Summary:
Addresses https://bugs.llvm.org/show_bug.cgi?id=43100

Formatting using statement in C# with clang-format removes the space between using and paren even when SpaceBeforeParens is !

```
using(FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, bufferSize : 1))
```

this change simply overcomes this for when using C# settings in the .clang-format file

```
using (FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, bufferSize : 1))
```

All FormatTests pass..

```
[==========] 688 tests from 21 test cases ran. (88508 ms total)
[  PASSED  ] 688 tests.
```

Reviewers: djasper, klimek, owenpan

Reviewed By: owenpan

Subscribers: llvm-commits, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66662

llvm-svn: 371720