Consolidate the nearest_index subroutines in FMS

[uramirez8707]

Is your feature request related to a problem? Please describe.
There are multiple subroutines in FMS that do the same thing:

• axis_utils::nearest_index - supports monotonically increasing array
• diag_utils::get_index - supports monotonically array
• horiz_interp_bilinear::indp - supports monotonically increasing array

Describe the solution you'd like
These subroutines should be consolidated into nearest_index in axis_utils and it should be expanded to support monotonically increasing and decreasing arrays

The modern diag manager is already using nearest_index

Describe alternatives you've considered
N/A

Additional context
This is to prepare for #1213