[clang-format] Handle C# property accessors when parsing lines

Summary:
Improve C# `{ get; set; } = default;` formatting by handling it in the UnwrappedLineParser rather than trying to merge lines later.

Remove old logic to merge lines.

Update tests as formatting output has changed (as intended).

Reviewers: krasimir, MyDeveloperDay

Reviewed By: krasimir

Subscribers: cfe-commits

Tags: #clang-format, #clang

Differential Revision: https://reviews.llvm.org/D78642