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/normal.c b/src/normal.c
index 81bedfd..b385c0d 100644
--- a/src/normal.c
+++ b/src/normal.c
@@ -2400,7 +2400,7 @@
     if (c == K_MOUSEMOVE)
     {
 	/* Mouse moved without a button pressed. */
-#ifdef FEAT_BEVALTERM
+#ifdef FEAT_BEVAL_TERM
 	ui_may_remove_balloon();
 	if (p_bevalterm && !VIsual_active)
 	{