input via maps: Removed _date/date filter from date fields because the main mappings now have _date around all dates, so this filter is redundant

inputs/SALVIAS-CSV/maps/VegCSV.organisms.csv: census_date: Don't map directly to the year, as this field is allowed to be a full date even though our data sample contains only years. Note that _date/date will automatically detect plain years and treat them as years, and so will casts to timestamp.

inputs/SALVIAS*/maps/VegCSV.organisms.csv: census_date: Documented that this is for the subplot, not the organism, as all organisms in a subplot have the same value for it

mappings/DwC2-VegBIEN.specimens.csv: verbatimLatitude/verbatimLongitude: Fixed mappings to use _alt/2 instead of _alt/1 to avoid collisions with decimalLatitude/decimalLongitude

schemas/functions.sql: _merge(): Changed sort_orders to match the $-variable name instead of the function parameter name, so each line of the VALUES clause would use the same number for both

schemas/functions.sql: _merge(): Filter out NULL values as optimization so DISTINCT ON only has to consider non-NULL values

schemas/functions.sql: join_strs(): Return NULL if all strings were NULL or ''. This fixes unexpected behavior in _merge() where all elements are NULL but the return value is non-NULL.

schemas/functions.sql: Added join_strs_transform_preserve_empty() and use it in join_strs_transform_fold_empty()

schemas/functions.sql: Renamed join_strs_() to join_strs_transform_fold_empty() for clarity and to indicate that it's for use by the join_strs() aggregate

mappings/DwC2-VegBIEN.specimens.csv: recordNumber: Added VegCSV mappings for it