A large portion of the VTK-m filters are now compiled into the
vtkm_filter library. These pre-built filters now don't include
the respective hxx file to remove the amount of template
instantiation users do.
To verify that this removal reduces compiler memory ( and maybe time)
I profiled the compiler while it building filter tests in debug mode.
Here is a selection of results:
```
CleanGrid 10.25s => 9.01s, 901MB => 795MB
ExternalFaces 13.40s => 5.96s, 1122MB => 744MB
ExtractStructured 4.69s => 4.75s, 492MB => 492MB
GradientExplicit 22.97s => 5.88s, 1296MB => 740MB
```
- It explicitly instantiate its concrete templates to
the supported types.
- It disables implicit template instantations for the
the supported types.
- Also fix small typo in Contour impl include guards
Signed-off-by: Vicente Adolfo Bolea Sanchez <vicente.bolea@kitware.com>
