[clang-format] Handle quotes and escaped braces in C# interpolated strings

Summary:
This addresses issues raised in https://bugs.llvm.org/show_bug.cgi?id=44454.

There are outstanding issues with multi-line verbatim strings in C# that will be addressed in a follow-up PR.

Reviewers: krasimir, MyDeveloperDay

Reviewed By: krasimir, MyDeveloperDay

Subscribers: MyDeveloperDay

Tags: #clang-format

Differential Revision: https://reviews.llvm.org/D73492