enable the negative version of the fates_recruit_init_density with non-nocomp types of runs

[rgknox]

For model cold-starts, there are two approaches to initializing stand structure without access to datasets, using the fates_recruit_init_density parameter:

https://github.com/NGEET/fates/blob/main/parameter_files/fates_params_default.cdl#L514

A positive value sets the abundance and assumes recruit sizes. A negative value sets the size (dbh) and assumes the plants fill the canopy. However, we only allow the negative method for nocomp scenarios. With nocomp, we can use the surface file datasets to determine how much of the canopy the different PFTs get.

This issue is a "wish-list" item, to enable the negative version of the fates_recruit_init_density with non-nocomp types of runs. Here, we would use the surface file to decide on canopy fractions, but only for the initial condition and would break from the fraction specified in the dataset immediately after in favor of fractions that manifest from dynamics.

[rgknox]

Note, the motivation for this feature was to increase robustness of our model testing. Others also expressed interest in using this capability to test model spin-up.