ddr: add support for analog axis-only pads and handle left+right / up+down input (#659)

## Link to GitHub Issue or related Pull Request, if one exists
n/a

## Description of change
Some crappy DDR soft mats (either USB-based or console pads with crappy
adapters that lack a dedicated "DDR pad mode") use X and Y analog axis
for arrows, which means they cannot cleanly report Up+Down or Left+Right
input.

According to some ancient Stepmania code, a lot of these report a middle
value (value between center and right, for example, for left+right).
Borrow this hack from Stepmania and implement it in spice as analog
input for DDR.

Also, for rawinput/xinput automatic bind scenario, update the logic so
that face buttons are always detected before analog axis / dpads for
consistency. This would help with binding any DDR pads that
simultaneously input face buttons / dpad / analog axis, so that we can
prefer face buttons when detected.

## Testing
I don't have any soft mats that have this, but it was tested with an
xbox controller.

src/spice2x/games/io.cpp

@@ -92,6 +92,9 @@ namespace games {
         games.push_back(ddr);
         buttons.insert({ ddr, ddr::get_buttons() });
         lights.insert({ ddr, ddr::get_lights() });
+        buttons_help.insert({ ddr, ddr::get_buttons_help() });
+        analogs_help.insert({ ddr, ddr::get_analogs_help() });
+        analogs.insert({ ddr, ddr::get_analogs() });
         file_hints[ddr].push_back({"ddr.dll"});
         file_hints[ddr].push_back({"mdxja_945.dll"});
         file_hints[ddr].push_back({"arkmdxp3.dll"});