patch 8.0.1312: balloon_show() only works in terminal when compiled with GUI

Problem:    balloon_show() only works in terminal when compiled with the GUI.
Solution:   Add FEAT_BEVAL_GUI and refactor to move common code out of the GUI
            specific file.
diff --git a/src/integration.c b/src/integration.c
index e61c5e3..064ff05 100644
--- a/src/integration.c
+++ b/src/integration.c
@@ -1077,7 +1077,7 @@
 }
 
 /* Send a message to eserve */
-#if defined(NOHANDS_SUPPORT_FUNCTIONS) || defined(FEAT_BEVAL)
+#if defined(NOHANDS_SUPPORT_FUNCTIONS) || defined(FEAT_BEVAL_GUI)
 void workshop_send_message(char *buf)
 {
 	dummy = write(sd, buf, strlen(buf));