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/ddr/io.cpp

@@ -35,6 +35,49 @@ std::vector<Button> &games::ddr::get_buttons() {
     return analogs;
 }
 
+
+std::string games::ddr::get_buttons_help() {
+    // keep to max 100 characters wide
+    return
+        "For DDR pad arrows, double check that simultaneous Left+Right and Up+Down can be detected.\n"
+        "You should boot the game, enter test menu, and use Foot Panel Check.\n\n"
+        "When mapping arrows, try the following in order:\n\n"
+        "  1. If your controller uses face buttons (A/B/X/Y), bind them here.\n"
+        "  2. If your controller supports XInput, use that.\n"
+        "  3. If your controller uses analog axis for arrows, try Analogs tab.\n"
+        "  4. Otherwise, you will need to use remapping software or get a better adapter."
+        ;
+}
+
+std::vector<Analog> &games::ddr::get_analogs() {
+    static std::vector<Analog> analogs;
+
+    if (analogs.empty()) {
+        analogs = GameAPI::Analogs::getAnalogs("Dance Dance Revolution");
+
+        GameAPI::Analogs::sortAnalogs(
+                &analogs,
+                "P1 Left-Right (Axis Fix)",
+                "P1 Up-Down (Axis Fix)",
+                "P2 Left-Right (Axis Fix)",
+                "P2 Up-Down (Axis Fix)"
+        );
+    }
+    return analogs;
+}
+
+std::string games::ddr::get_analogs_help() {
+    // keep to max 100 characters wide
+    return
+        "Only use this if your DDR pad outputs analog axis for arrows.\n\n"
+        "If the pad uses face buttons (A/B/X/Y), use Buttons tab instead.\n\n"
+        "Spice will treat values <=25% as Left, >=75% as Right, ~=50% as neutral,\n"
+        "and value between 50% and 75% as both arrows.\n\n"
+        "This is the classic Stepmania \"Axis Fix\" which may or may not work with\n"
+        "your dance pad or your adapter."
+        ;
+}
+
 std::vector<Light> &games::ddr::get_lights() {
     static std::vector<Light> lights;