Wait for index to be updated before workspace-wide operations like rename, call hierarchy and type hierarchy

[ahoppen]

It might make sense to wait for an up-to-date workspace wide index for global operations like rename, call hierarchy, or type hierarchy. The tricky part is how we communicate to the user if the task is taking longer than expected and how we make sure that the editor doesn’t cancel eg. rename because of a timeout.

rdar://127474967

[ahoppen]

This is actually really important because of the following scenario:

• A module has a function foo() that gets used in downstream modules
• Now the declaration of foo is modified to foo(x: Int = 1).
• The USR of foo has changed but we don’t have any references in the index to the new USR because the other modules haven’t been re-indexed yet.