Parser: Add ability to read in generic blocks

[uramirez8707]

Description
Adds three new subroutines to the parser:

public :: get_num_unique_blocks
public :: get_unique_block_ids
public :: get_block_name

These are needed in order to read the new format of the field table yaml described in #1520

Fixes #1520

How Has This Been Tested?
CI, including new test

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes

[uramirez8707]

@J-Lentz @GFDL-Eric
This is relevant code that will be used to read the new field_table yaml format.
get_num_unique_blocks is going to be used to get the number of unique blocks for each variable. For the example below, it will get 1 for sphum and 2 for soa. get_unique_block_ids will be used to get an id for each of the blocks and that can be used to get the block name (i.e profile_type for sphum, and chem_param and profile_type for soa) and from there, it can be read as normal ...

field_table:
- field_type: tracer
  modlist:
  - model_type: atmos_mod
    varlist:
    - variable: sphum
      longname: specific humidity
      units: kg/kg
      profile_type:
      - value: fixed
        surface_value: 3.0e-06
    - variable: soa
      longname: SOA tracer
      units: mmr
      convection: all
      chem_param:
      - value: aerosol
      profile_type:
      - value: fixed
        surface_value: 1.0e-32