Add Dolphin-compatible input expressions and GCPadNew.ini import, DualSense L/R remapping, vibration toggle (#89)

* Add Dolphin-compatible input expressions and GCPadNew.ini import

Rebased onto current main; addresses both CodeRabbit reviews on #89.

- Expression engine matching Dolphin's semantics: doubles rather than
  booleans, 0.5 press threshold, & as min, | as max, and the functions if,
  min, max, clamp, abs, sqrt, pow, sin, cos, tan, deadzone, timer, toggle,
  hold, tap, pulse and smooth. Timing uses a steady clock in seconds, as
  Dolphin does, so a copied expression behaves identically.

- Expressions bind to the GameCube buttons and triggers, combined with the
  existing button mapping rather than replacing it, and are skipped while
  the settings overlay holds input.

- Import reads [GCPadN] from the Dolphin config directory or from
  GCPadNew.ini beside the executable. Stick axes are not expression driven
  and keep their normal mapping.

- Fixes #74: a digital button bound to L or R now reports a fully pulled
  analog trigger, plus a PlayStation preset and a vibration toggle.

Review fixes: config paths round-trip through RuntimeConfigFile::PathToUtf8
and PathFromUtf8 so non-ASCII paths open correctly on Windows, and the
duplicated exists branch is gone; the tap count is clamped before the
unsigned conversion; the expression editor uses resizable storage via
ImGuiInputTextFlags_CallbackResize so a long expression cannot be saved
truncated; clamp bounds are ordered before std::clamp; <cstdlib> is included
for std::strtod; non-finite values are rejected at the evaluator boundary as
well as at the deadzone and timer divisions; and InputBindings::Reload() runs
from InitializeRuntimeSettings rather than the vibration handler.

runtime/tests/test_expr.cpp covers operator precedence, each stateful
function and every case raised in review.

Third review round: smooth() guards NaN as well as infinity so a zero rate
cannot latch a non-finite value in node state; division evaluates both operands
so stateful functions in the left subtree still update when the divisor is zero;
the expression editor clears stale errors when the port changes; and
runtime/tests/test_expr.cpp is registered with CTest as mkw_input_expr_tests,
following the existing test targets.

* Update runtime/src/input_expr.cpp

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

* Update runtime/src/input_expr.cpp

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

* Update runtime/src/input_expr.cpp

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

runtime/include/runtime_config.h

@@ -11,6 +11,7 @@
 #include <iomanip>
 #include <iostream>
 #include <limits>
+#include <map>
 #include <optional>
 #include <sstream>
 #include <string>
@@ -89,6 +90,8 @@ struct RuntimeUserConfig {
     // comma-separated SDL-style physical button names ("south", or
     // "dpad_up,left_shoulder") as values; pressing either bound button counts.
     std::array<std::optional<std::string>, 12> controllerButtons;
+    std::optional<bool> rumbleEnabled;
+    std::map<std::string, std::string> controllerExpressions;
 };
 
 namespace RuntimeConfigFile {
@@ -407,6 +410,17 @@ inline RuntimeUserConfig ParseConfigDocument(const toml::value& document) {
             FindConfigValue<std::string>(document, "controller", buttonKeys[index]);
     }
 
+    config.rumbleEnabled = FindConfigValue<bool>(document, "controller", "rumble");
+
+    if (const auto* section = document.contains("controller") ? &document.at("controller") : nullptr;
+        section != nullptr && section->is_table()) {
+        for (const auto& [key, value] : section->as_table()) {
+            if (key.rfind("expr_", 0) == 0 && value.is_string()) {
+                config.controllerExpressions[key] = value.as_string();
+            }
+        }
+    }
+
     config.widescreen = FindConfigValue<bool>(document, "video", "widescreen");
     config.windowPosX = FindConfigInt(document, "video", "window_x");
     config.windowPosY = FindConfigInt(document, "video", "window_y");
@@ -677,6 +691,25 @@ inline bool SetControllerButton(size_t index, std::string value) {
     return WriteSetting("controller", kControllerButtonKeys[index], FormatString(value));
 }
 
+inline std::string ControllerExpression(const std::string& key) {
+    const auto it = Get().controllerExpressions.find(key);
+    return it == Get().controllerExpressions.end() ? std::string() : it->second;
+}
+
+inline bool SetControllerExpression(const std::string& key, const std::string& value) {
+    Mutable().controllerExpressions[key] = value;
+    return WriteSetting("controller", key, FormatString(value));
+}
+
+inline bool RumbleEnabled(bool fallback = true) {
+    return Get().rumbleEnabled.value_or(fallback);
+}
+
+inline bool SetRumbleEnabled(bool value) {
+    Mutable().rumbleEnabled = value;
+    return WriteSetting("controller", "rumble", value ? "true" : "false");
+}
+
 inline bool SetAudioVolume(float value) {
     value = std::clamp(value, 0.0f, 1.0f);
     Mutable().audioVolume = value;