[FEA] Add initial support for CreateMap

[andygrove]

Is your feature request related to a problem? Please describe.
I would like to be able to create Map types on the GPU. For example:

spark.sql("select map(name,name) as newmap from df1")

Describe the solution you'd like
Create a GpuCreateMap expression.

Describe alternatives you've considered
None

Additional context
This is part of #44