Multiple `filters.expression` => multiple PointView

[Howard Butler]

It would be handy to explode expressions into different PointViews in a single filters.expression invocation. The following example would split the input stream into three different PointViews. The purpose of this might be to save multiple passes through data for further filtering in Python, for example.

  {
    "type": "filters.expression",
     "expression": [
      "Classification == 2",
      "ReturnNumber == 1 && NumberOfReturns == 1 ReturnNumber < 1",
      "ReturnNumber == 1 & NumberOfReturns > 1"
    ]
  },

[Howard Butler]

Implemented in #4328 4328