Fix #421 present the text/plain;charset=utf-8 to the wayland clipboard

Enables copy from eclipse to KDE/QT apps in a wayland session(RFC-1341)

bundles/org.eclipse.swt/Eclipse SWT Drag and Drop/gtk/org/eclipse/swt/dnd/ClipboardProxy.java

@@ -169,6 +169,9 @@ boolean setData(Clipboard owner, Object[] data, Transfer[] dataTypes, int clipbo
 				System.arraycopy(entries, 0, tmp, 0, entries.length);
 				tmp[entries.length] = entry;
 				entries = tmp;
+				TransferData tdata = new TransferData();
+				tdata.type = typeIds[j];
+				transfer.javaToNative(data[i], tdata);
 			}
 		}
 

bundles/org.eclipse.swt/Eclipse SWT Drag and Drop/gtk/org/eclipse/swt/dnd/TextTransfer.java

@@ -13,6 +13,8 @@
  *******************************************************************************/
 package org.eclipse.swt.dnd;
 
+import java.nio.charset.*;
+
 import org.eclipse.swt.internal.*;
 import org.eclipse.swt.internal.gtk.*;
 
@@ -109,8 +111,29 @@ public void javaToNative (Object object, TransferData transferData) {
 		transferData.pValue = string_target;
 		transferData.result = 1;
 	}
+    if (transferData.type == TEXT_PLAIN_UTF8_ID) {
+        // Convert the text into RFC-1341 format
+        byte[] rfc1341Data = encodeTextAsRFC1341(string);
+        transferData.format = 8; // Format for UTF-8
+        transferData.length = rfc1341Data.length;
+        transferData.pValue = OS.g_malloc(rfc1341Data.length);
+        if (transferData.pValue != 0) {
+            C.memmove(transferData.pValue, rfc1341Data, rfc1341Data.length);
+            transferData.result = 1;
+        }
+    }
+}
+
+// New method to encode text as RFC-1341
+private byte[] encodeTextAsRFC1341(String text) {
+    // Implement encoding logic here, e.g., adding MIME headers and encoding text
+    // This is a simplified example; actual encoding depends on RFC-1341 standards
+//    String rfc1341Text = "Content-Type: " + TEXTPLAINUTF8 + "\r\n\r\n" + text;
+    String rfc1341Text = text;
+    return rfc1341Text.getBytes(StandardCharsets.UTF_8);
 }
 
+
 /**
  * This implementation of <code>nativeToJava</code> converts a platform specific
  * representation of plain text to a java <code>String</code>.