[clang] [Clang] Propagate elide safe context through [[clang::coro_must_await]] (PR #108474)

[Adrian Vogelsgesang via cfe-commits]

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@@ -8261,12 +8261,19 @@ def CoroAwaitElidableDoc : Documentation {
 The ``[[clang::coro_await_elidable]]`` is a class attribute which can be applied
 to a coroutine return type.
----------------
vogelsgesang wrote:

```suggestion
to a coroutine return type. It provides a hint to the compiler to apply Heap Allocation Elision
more aggressively.
```

I like it if the first paragraph of any documentation immediately gives me a high-level picture, so I know if I should keep reading the rest of its documentation or skip it. By immediately mentioning Heap Allocation Elision in the first paragraph, the reader also gets more context when read the rest of the paragraph, so he will hopefully be able to understand the following paragraphs more easily

https://github.com/llvm/llvm-project/pull/108474