lavfi/curves: add forgotten strong_contrast preset.

doc/filters.texi

@@ -2355,6 +2355,7 @@ Available presets are:
 @item linear_contrast
 @item medium_contrast
 @item negative
+@item strong_contrast
 @item vintage
 @end table
 Default is unset.

libavfilter/vf_curves.c

@@ -91,6 +91,11 @@ static const struct {
         "0.286/0.219 0.639/0.643",
     },{
         "negative", "0/1 1/0", "0/1 1/0", "0/1 1/0",
+    },{
+        "strong_contrast",
+        "0.301/0.196 0.592/0.6 0.686/0.737",
+        "0.301/0.196 0.592/0.6 0.686/0.737",
+        "0.301/0.196 0.592/0.6 0.686/0.737",
     },{
         "vintage",
         "0/0.11 0.42/0.51 1/0.95",