overlay: UI scaling option (#495)

## Link to GitHub Issue, if one exists
#477 

## Description of change
Add a new option for scaling the overlay.

Gitadora Arena will receive 250% by default.

Various overlay windows have been updated to scale properly, not perfect
but they are at least usable.

src/spice2x/overlay/windows/iopanel.cpp

@@ -11,7 +11,7 @@ namespace overlay::windows {
         this->flags = ImGuiWindowFlags_AlwaysAutoResize;
 
         this->init_size = ImVec2(
-            80,
+            overlay::apply_scaling(80),
             ImGui::GetFrameHeight() +
                 ImGui::GetStyle().WindowPadding.y * 2 +
                 ImGui::GetFrameHeightWithSpacing() * 3 +
@@ -58,7 +58,7 @@ namespace overlay::windows {
     void IOPanel::build_io_panel() {}
 
     void IOPanel::build_operator_menu() {
-        const ImVec2 wide(60, 0);
+        const ImVec2 wide = overlay::apply_scaling_to_vector(60, 0);
         const float spacing_x = ImGui::GetStyle().ItemSpacing.y;
         const ImVec2 tall(
             ImGui::GetFrameHeight(),