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/version.c b/src/version.c
index 87f922f..c0ed2bf 100644
--- a/src/version.c
+++ b/src/version.c
@@ -88,12 +88,12 @@
 #else
 	"-autoservername",
 #endif
-#ifdef FEAT_BEVAL
+#ifdef FEAT_BEVAL_GUI
 	"+balloon_eval",
 #else
 	"-balloon_eval",
 #endif
-#ifdef FEAT_BEVALTERM
+#ifdef FEAT_BEVAL_TERM
 	"+balloon_eval_term",
 #else
 	"-balloon_eval_term",
@@ -772,6 +772,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1312,
+/**/
     1311,
 /**/
     1310,