Cache Annotation Lookups

[jzheaux]

Several Security components use SecurityAnnotationScanners to look for annotations and apply Security's expression template support and enforce its uniqueness constraints.

Given that this is used by a number of method interceptors and AOT hints, it would be nice if the found merged annotations were cached. Indeed, the JavaDoc encourages this:

/**
  * Since the process of synthesizing an annotation can be expensive, it's recommended to
  * cache the synthesized annotation to prevent multiple computations.
  */