This change removes the extendable AStoreable node from the Painless user tree. AStoreable was used to determine if a node was allowed to store a value. However, this was fragile and inflexible as the instanceof check was only 1-level deep so nodes still could throw errors under certain circumstances. This has been replaced by an expression input "write" to tell an expression node whether or not it is meant to store a value. This allows expressions nodes to determine the best course of action when asked to store a value and also gives better error messaging.

This also makes isDefOptimized an output of an expression as opposed to a mutable value on an expression. This is used to determine if a def method returning a value can change the returned value as part of the method signature as opposed to an extra cast.