With the major revision 2.0 of VTK-m, many items previously marked as
deprecated were removed. If updating to a new version of VTK-m, it is
recommended to first update to VTK-m 1.9, which will include the deprecated
features but provide warnings (with the right compiler) that will point to
the replacement code. Once the deprecations have been fixed, updating to
2.0 should be smoother.
For several versions, VTK-m has had a `Variant` templated class. This acts
like a templated union where the object will store one of a list of types
specified as the template arguments. (There are actually 2 versions for the
control and execution environments, respectively.)
Because this is a complex class that required several iterations to work
through performance and compiler issues, `Variant` was placed in the
`internal` namespace to avoid complications with backward compatibility.
However, the class has been stable for a while, so let us expose this
helpful tool for wider use.
Rather than try to collect all `LastCell` types inside of a single
header and make an uber type, have each cell locator define its own cell
locator type and use that.
`PointLocator`s have changed from being virtual objects to being trivial
objects. Part of this change means that when a worklet gets the
execution object for a point locator, it gets the actual object (or a
reference to it) instead of a pointer to an object. This means that the
new code uses the `.` operator to access the locator's features instead
of the `->` operator.
To support code still using the deprecated functionality, added a
specific `->` operator to the locator execution object to make it behave
as if it were a pointer. However, this operator is marked deprecated to
warn the user that they should modify their code to use the `.` instead.
Deprecated the `CellLocator` class and made all methods of the
other `CellLocator` classes non-virtual. General locators can
still use the `CellLocatorGeneral` class, but this class now
only works with a predefined set of locators. (The functionality
to provide a function to select a locator has been removed.)
