change taskcanceledexception to operationcanceledexception

[taooceros]

fix #357

[taooceros]

I originally think that taskcancelledexception may be thrown by task cancellation token, but in reality it throws an operation canceledexception. Therefore, we should also change some place where using TaskCancelledException for handling. We do use OperationCanceledException else where due to compatibility except websearch plugin.

[jjw24]

except websearch plugin.

Do we need to update websearch too?

We do use OperationCanceledException else where...

Sounds strange, how are we going to differentiate task cancelled and actual error from operation cancelled?

[taooceros]

I just read some new change toward HttpClient, and they seems not wrap a Timeout exception within the TaskCanceledException.
Check out the discussion here dotnet/runtime#21965
and the pr here dotnet/runtime#2281
I don't know why the error trace from @solymr is actually OperationCanceledException. That's weird, because it supposed to be a taskcenceledexception when timeout.

Our original OperationCanceledException is for one excpetion handling for both taskcanceledexception and parallel exercution canceled exception.

[taooceros]

Based on the discussion there and the pr, we should distinguish this by checking whether innerexception is timeoutexception.

[taooceros]

emmm seems that that pr is for .Net 5, so we can only do that after upgrading to .net 5

[jjw24]

if we get more users reporting this issue, then we can do a hotfix