schemas/vegbien.sql: location: documented `CREATE INDEX plot_source_id` runtime (5 min)

fix: schemas/vegbien.sql: location: added plot_source_id index to provide the equivalent of the location.source_id index for outer plots. this will help Postgres choose the right query plans in queries involving outer plots.

schemas/vegbien.sql: _plots_18_list_of_subplots_codes_for_each_plot_for_each_project: added ~type table

schemas/vegbien.sql: _plots_15_pct_cover_of_each_verb_taxon_in_each_plot_in_each_pro: added ~type table

bugfix: schemas/Makefile: `%/install: vegbien.sql`: also need to match `public_validations` when used as a schema-qualifier (public_validations._), and after a cast (::) to a schema-qualified type. these occur in schema-qualified casts to the custom return type in the keys() functions.

bugfix: schemas/Makefile: `%/install: vegbien.sql`: sed expr: need to use '' instead of "" because $(*q) may contain "

bugfix: schemas/vegbien.sql: _plots_10a_aggregate_observation_individual_counts: need to use taxonoccurrence.sourceaccessioncode, not aggregateoccurrence.sourceaccessioncode, because aggregateoccurrence.sourceaccessioncode is not populated

schemas/vegbien.sql: public_validations schema comment: documented how to remove a validations query so its columns can be changed (use public_validations.rm_query_view())

schemas/vegbien.sql, inputs/SALVIAS/validations.sql: added _plots_10a_aggregate_observation_individual_counts, for use in debugging diffs in _plots_10_count_of_individuals_per_plot_in_each_proj

schemas/util.sql: create_if_not_exists(): also support `CREATE FUNCTION` (by handling duplicate_function exceptions)