[clang] [docs][coroutines] Revamp "Debugging C++ coroutines" (PR #142651)

[Adrian Vogelsgesang via cfe-commits]

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@@ -8,470 +8,966 @@ Debugging C++ Coroutines
 Introduction
 ============
 
-For performance and other architectural reasons, the C++ Coroutines feature in
-the Clang compiler is implemented in two parts of the compiler.  Semantic
-analysis is performed in Clang, and Coroutine construction and optimization
-takes place in the LLVM middle-end.
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vogelsgesang wrote:

I merged this now, since I want to be able to point people to the documentation from a discourse thread. Let me know if I missed anything. Happy to update this further also post-commit

https://github.com/llvm/llvm-project/pull/142651