Update Steam path detection for Linux (#21948)

* Update Steam path detection for Linux

As Steam now uses Proton to install Windows version natively, update
paths so they get found automatically

* Use new Steam path detection on Linux only

This restores Steam path detection on macOS as it doesn't have Proton

src/openrct2/platform/Platform.Android.cpp

@@ -151,6 +151,16 @@ namespace Platform
         return {};
     }
 
+    u8string GetRCT1SteamDir()
+    {
+        return {};
+    }
+
+    u8string GetRCT2SteamDir()
+    {
+        return {};
+    }
+
 #    ifndef NO_TTF
     std::string GetFontPath(const TTFFontDescriptor& font)
     {