Allow CallStacks to be hidden or cut

This is a spin off of #11035. I’d like to see a way for a function foo

• use another function bar with a (?_::CallStack) constraint so that bar will not print a call stack, and
• use another function bar with a (?_::CallStack) constraint so that if bar prints a call stack, it will stop at the call to foo.

This might be possible to implement with a special rootCallStack :: CallStack which is a value such that

x `pushCallStack` rootCallStack = rootCallStack

but

rootCallStack `pushCallStack` x = rootCallStack “:” x

as before and a call stack that consists of only a rootCallStack causes no stack trace to be printed.

The use case is to provide the user of a library less cluttered call stacks that do not expose unhelpful details and allow her to quickly spot the relevant information.

Trac metadata

Trac field	Value
Version	7.10.2
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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