Decoration API: Add lightweight ability to have complete coverage (#7456)

Decoration API: Add lightweight ability to have complete coverage (#7456)

When the noise value or fill_ratio >= 10.0 complete coverage is enabled.
This disables random placement to avoid redundant multiple placements
at one position. Instead, 1 decoration per surface node is placed by
looping across each division.

'10' was chosen as this is the fill_ratio that previously created
very near complete coverage. The complete coverage feature therefore
integrates smoothly when noise is used for variable decoration density.

'fill_ratio = 10' should be used by modders who want a decoration
placed on every surface node. Compared to before such a decoration
placement will be 10 times faster.