Add functions to recursively fill `Fields`

[imreddyTeja]

ClimaCore.RecursiveApply.rzero can zero a Tuple containing a DiagonalMatrixRow of AxisTensors. There is no equivalent way to fill it with any other value. There should be a function that does this for all types that rzero supports. Additionally, rmap does not behave as expected. For example, it does not map into AxisTensors