GEOMESA-418 Time-enabled layer previews are not handled optimally

Recognizing binary inequality filters involving canonical time variable as temporal filters and handling them like before/after.
I see this was already there, but I'm curious why TEQUALS isn't supported... Seems like it should be. See https://github.com/locationtech/geomesa/blob/accumulo1.5.x/1.x/geomesa-core/src/test/scala/org/locationtech/geomesa/core/index/AttributeIndexStrategyTest.scala#L244