overlay: simplify various input controls by introducing new custom ImGUI widgets (#536)

## Description of change

* Add a red `x` button to replace `Clear` button in binding tabs
(Buttons/Analog/Lights).
* Add a gray `x` button to replace `Clear` button in options tabs next
to input widgets
* Add helper for truncating text and adding ellipsis (...) to deal with
text overflow in tables.
* Reword some UI text for clarity

src/spice2x/overlay/imgui/extensions.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <string>
+
 namespace ImGui {
 
     void HelpTooltip(const char* desc);
@@ -7,6 +9,12 @@ namespace ImGui {
     void WarnTooltip(const char* desc, const char* warn);
     void WarnMarker(const char* desc, const char* warn);
     void DummyMarker();
+
     void Knob(float fraction, float size, float thickness = 2.f,
             float pos_x = -1.f, float pos_y = -1.f);
+
+    std::string TruncateText(const std::string& p_text, float p_truncated_width);
+    bool AddButton(const std::string& tooltip);
+    bool DeleteButton(const std::string& tooltip);
+    bool ClearButton(const std::string& tooltip);
 }