Add dialog or option to Linear Line of Sight tool to give user option to select his observer and target heights

[NatalieCampos]

Provide a dialog to the user to allow the user to select their own Height Above Surface or Offset fields from their Targets and Observer features. As is currently the Add Linear Line of Sight Fields GP tool is a precursor to the Linear Line of Sight tool. However, currently there is a disconnect between the two tools as the output from the Add Linear Line of Sight Fields does not produce an output that the Linear Line of Sight tool accepts. Running the two tools sequentially will result in the Linear Line of Sight tool to fail.

ETA: the tool does work with the features sets...this request is for the use of the tool with already existent features.

Steps to Reproduce (for bugs)

1. Run Add Linear Line of Sight Fields
2. Run Linear Line of Sight
3. LLOS will fail

We would like

We would like

Option A:

1. Run Linear Line of Sight where the user can choose a field for HGT or Offset within their attribute table for both their target and observer pts. This will make the requirement of running the Add Linear Line of Sight Fields unnecessary.

Option B:

1. Run Add Linear Line of Sight Fields - correct fields are added for use in next tool
2. Run Linear Line of Sight