[HeapViewer] Sample different elements from large arrays when inspecting a heap dump

[thurka]

Reported internally, description below:

When inspecting a large array in a heap dump, VisualVM allows to sample 100 random elements from the array, which is a nice feature. When the "<sample 100 items>" tree node is collapsed and expanded, always the same 100 items are being displayed (i.e., the items are cached).
It would be great if there was a way to retrigger the sampling so that another batch of 100 array elements is displayed.

[thurka]

Done in master.