Represents a request to link a particular invocation at a particular call
site. Instances of these requests will be constructed and passed to all
GuardingDynamicLinker objects managed by the DynamicLinker
that is trying to link the call site.
Returns true if the call site is considered unstable, that is, it has been relinked more times than was
specified in DynamicLinkerFactory.setUnstableRelinkThreshold(int). Linkers should use this as a
hint to prefer producing linkage that is more stable (its guard fails less frequently), even if that assumption
causes a less effective version of an operation to be linked. This is just a hint, though, and linkers are
allowed to ignore this property.