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/popupmnu.c b/src/popupmnu.c
index dc66e75..82e3ef7 100644
--- a/src/popupmnu.c
+++ b/src/popupmnu.c
@@ -760,7 +760,7 @@
     return pum_height;
 }
 
-# if defined(FEAT_BEVALTERM) || defined(PROTO)
+# if defined(FEAT_BEVAL_TERM) || defined(PROTO)
 static pumitem_T *balloon_array = NULL;
 static int balloon_arraysize;
 static int balloon_mouse_row = 0;