Provide a different style treatment for overlapping wetland and forest (i.e., `natural=wetland` and `wetland=swamp`)

[jeffreyameyer]

Style change requested

Apparently, a swamp is a forested wetland. I hadn't really thought about that before mapping some, although it makes perfect sense.

Unfortunately, our currently stylesheets force an either-or choice: either swamps are depicted as forests, or as wetlands.

See here:

and here:

Neither of these treatments seems ideal, as swamps play a much different role in human impact on the earth (why bother deforesting a swamp if you still have to drain the wetland?) as well as in human history (swamps as escape routes for enslaved people, who even set up entire towns in swamps, etc.).

For example, if you looked at modern satellite image, it might not catch your eye as to why exactly, these forests have been reduced to lumber and what might be nice riverside real estate hasn't been exploited:

The USGS National Map has a treatment that blends both iconography for wetlands and color for forests to indicate swamps:

Now... these areas are also tagged as wetland=swamp, which may be a needed tag in the vtiles, to differentiate from wetland=marsh or just plain old natural=wetland without wetland=* for coast areas like here:

Small side comment: imo, the USGS marshland sprite:

is much more fun than ours:

[vknoppkewetzel]

Alright, I have created a pattern that I think 🤞 will work.

Next steps: 1) find the best color to work for this pattern in OHM style (currently just colored random green for testing purposes) 2) get into spritesheet and style itself and review in maputnik 3) review in staging style to confirm it looks good after 1 and 2