[clang-format] Merge name and colon into a single token for C# named arguments

Summary:
Merge 'argumentName' and ':' into a single token in foo(argumentName: bar).

Add C# named argument as a token type.

Reviewers: krasimir, MyDeveloperDay

Reviewed By: krasimir

Tags: #clang-format

Differential Revision: https://reviews.llvm.org/D74894