Go to Definition on includes can get stuck due to hover or documentHighlight requests that are stuck on IntelliSense updating (from document switching)

Discussed in https://github.com/microsoft/vscode-cpptools/discussions/8881

^{Originally posted by juxeii February 18, 2022}
We have a very large code base.
One problem I have with Intellisense is that it reparses the active document although it has been parsed before.
Here is an example of how I cannot work in a smooth fashion:
I mark one include file A and click "Go to Definition".
The file A opens in an instant which is fine.
Now I go back to the original file from where I jumped from and browse to other include files.
Now I want to browse to file A again(no changes were made). It can take many seconds now to open the file A again.

I wonder why is that? Why is there no cache used which opens the file A again in an instant?
On the console for C/C++ I can see "idle loop: reparsing the active document".
Is there something I can do to improve the user experience here?

Start with the linked discussion #8881 and the C/C++ extension's handling of IntelliSense hover, documentHighlight, and Go to Definition requests. Reproduce the document-switching sequence; done means these requests do not remain stuck while IntelliSense updates and repeated navigation no longer waits several seconds.