Support swapping the functionality of the front buttons (#133)

## Summary

**What is the goal of this PR?** 

Adds a setting to swap the front buttons. The default functionality are:
Back/Confirm/Left/Right. When this setting is enabled they become:
Left/Right/Back/Confirm. This makes it more comfortable to use when
holding in your right hand since your thumb can more easily rest on the
next button. The original firmware has a similar setting.

**What changes are included?**

- Add the new setting.
- Create a mapper to dynamically switch the buttons based on the
setting.
- Use mapper on the various activity screens.
- Update the button hints to reflect the swapped buttons.

## Additional Context

Full disclosure: I used Codex CLI to put this PR together, but did
review it to make sure it makes sense.

Also tested on my device:
https://share.cleanshot.com/k76891NY

src/MappedInputManager.cpp

@@ -0,0 +1,77 @@
+#include "MappedInputManager.h"
+
+decltype(InputManager::BTN_BACK) MappedInputManager::mapButton(const Button button) const {
+  const auto layout = static_cast<CrossPointSettings::FRONT_BUTTON_LAYOUT>(SETTINGS.frontButtonLayout);
+
+  switch (button) {
+    case Button::Back:
+      switch (layout) {
+        case CrossPointSettings::LEFT_RIGHT_BACK_CONFIRM:
+          return InputManager::BTN_LEFT;
+        case CrossPointSettings::BACK_CONFIRM_LEFT_RIGHT:
+        default:
+          return InputManager::BTN_BACK;
+      }
+    case Button::Confirm:
+      switch (layout) {
+        case CrossPointSettings::LEFT_RIGHT_BACK_CONFIRM:
+          return InputManager::BTN_RIGHT;
+        case CrossPointSettings::BACK_CONFIRM_LEFT_RIGHT:
+        default:
+          return InputManager::BTN_CONFIRM;
+      }
+    case Button::Left:
+      switch (layout) {
+        case CrossPointSettings::LEFT_RIGHT_BACK_CONFIRM:
+          return InputManager::BTN_BACK;
+        case CrossPointSettings::BACK_CONFIRM_LEFT_RIGHT:
+        default:
+          return InputManager::BTN_LEFT;
+      }
+    case Button::Right:
+      switch (layout) {
+        case CrossPointSettings::LEFT_RIGHT_BACK_CONFIRM:
+          return InputManager::BTN_CONFIRM;
+        case CrossPointSettings::BACK_CONFIRM_LEFT_RIGHT:
+        default:
+          return InputManager::BTN_RIGHT;
+      }
+    case Button::Up:
+      return InputManager::BTN_UP;
+    case Button::Down:
+      return InputManager::BTN_DOWN;
+    case Button::Power:
+      return InputManager::BTN_POWER;
+    case Button::PageBack:
+      return InputManager::BTN_UP;
+    case Button::PageForward:
+      return InputManager::BTN_DOWN;
+  }
+
+  return InputManager::BTN_BACK;
+}
+
+bool MappedInputManager::wasPressed(const Button button) const { return inputManager.wasPressed(mapButton(button)); }
+
+bool MappedInputManager::wasReleased(const Button button) const { return inputManager.wasReleased(mapButton(button)); }
+
+bool MappedInputManager::isPressed(const Button button) const { return inputManager.isPressed(mapButton(button)); }
+
+bool MappedInputManager::wasAnyPressed() const { return inputManager.wasAnyPressed(); }
+
+bool MappedInputManager::wasAnyReleased() const { return inputManager.wasAnyReleased(); }
+
+unsigned long MappedInputManager::getHeldTime() const { return inputManager.getHeldTime(); }
+
+MappedInputManager::Labels MappedInputManager::mapLabels(const char* back, const char* confirm, const char* previous,
+                                                         const char* next) const {
+  const auto layout = static_cast<CrossPointSettings::FRONT_BUTTON_LAYOUT>(SETTINGS.frontButtonLayout);
+
+  switch (layout) {
+    case CrossPointSettings::LEFT_RIGHT_BACK_CONFIRM:
+      return {previous, next, back, confirm};
+    case CrossPointSettings::BACK_CONFIRM_LEFT_RIGHT:
+    default:
+      return {back, confirm, previous, next};
+  }
+}