Include effString2Parameter in opcode list

We don't need any special handling for this since our default argument
detection will handle strings, but it might be useful for log output if
a host ever uses this. At the moment there don't seem to be any hosts on
Linux that use this.

src/common/logging/vst2.cpp

@@ -156,6 +156,9 @@ std::optional<std::string> opcode_to_string(bool is_dispatch, int opcode) {
             case effGetSpeakerArrangement:
                 return "effGetSpeakerArrangement";
                 break;
+            case effString2Parameter:
+                return "effString2Parameter";
+                break;
             case effVendorSpecific:
                 return "effVendorSpecific";
                 break;
@@ -356,7 +359,8 @@ void Vst2Logger::log_set_parameter_response() {
     }
 }
 
-void Vst2Logger::log_event(bool is_dispatch,
+void Vst2Logger::log_event(
+    bool is_dispatch,
     int opcode,
     int index,
     intptr_t value,

src/common/vst24.h

@@ -55,6 +55,14 @@
  */
 [[maybe_unused]] constexpr int effVendorSpecific = 50;
 
+/**
+ * Set a parameter based on a string, kind of the inverse of the inverse of
+ * `effGetParamDisplay()` and an alternative to `setParameter()`. Also found in
+ * the list in Carla's repo. It's used in this way in JUCE here:
+ * https://github.com/juce-framework/JUCE/blob/b34e798f392179caf9c67dce273398fa03352067/modules/juce_audio_plugin_client/VST/juce_VST_Wrapper.cpp#L927
+ */
+[[maybe_unused]] constexpr int effString2Parameter = 27;
+
 /**
  * Used by hosts to query the length of reverb tails (equivalent to
  * `IAudioProcessor::getTailSamples`). Found on the same list as above.