fix: make Jni::FreeTrueUtf8 const-safe

TextEditor/TextEditorLanguageDefinition use 'const char* value =
env->GetStringUTFChars(...)' then release via the same pointer. After
the mass replace the release side called FreeTrueUtf8(char*) with a
const char* argument, which fails to compile. Switch the helper
signature to take const char* so both const and non-const call sites
build.

imgui-binding/src/main/native/jni_common.cpp

@@ -161,7 +161,7 @@ namespace Jni
         return buf;
     }
 
-    void FreeTrueUtf8(char* p) {
-        if (p != nullptr) free(p);
+    void FreeTrueUtf8(const char* p) {
+        if (p != nullptr) free((void*)p);
     }
 }

imgui-binding/src/main/native/jni_common.h

@@ -54,5 +54,5 @@ namespace Jni
     // the glyph atlas even when the glyph is registered. Caller must release with
     // FreeTrueUtf8(). Returns nullptr iff the input jstring is null.
     char* ToTrueUtf8(JNIEnv* env, jstring s);
-    void FreeTrueUtf8(char* p);
+    void FreeTrueUtf8(const char* p);
 }