Update CoroutineScope() factory documentation

[qwwdfsad]

Fixes #2891

[dkhalanskyjb]

Sure.

just like inside [coroutineScope] block.

Maybe it's also worth it to explicitly mention in the coroutineScope documentation that cancelling the scope also cancels the children? The only mention of this behaviour that I see is fairly indirect:

• 3. If the outer scope of showSomeData is cancelled, both started async and withContext blocks are cancelled.

[qwwdfsad]

Honestly, I do not see how it can be fit organically.

We have quite extensive documentation in CoroutineScope and Job, while the rest of the builders (whether it is async or withContext) point to it. Not sure it's worth repeating in every declaration