VSE: add Cubic Mitchell filtering, rename previous cubic to Cubic BSpline

Part of overall "improve filtering situation" (#116980) task:

- Add "Cubic Mitchell" filtering option to VSE strips. This is a cubic
  (4x4) filter that generally looks better than bilinear, while not
  blurring the image as much as the Cubic BSpline filter that exists
  elsewhere within Blender. It is also default in many other apps.
- Rename the (very recently added) VSE Bicubic filter option to
  Cubic BSpline.

@@ -178,0 +199,4 @@
+    for (int i = 0; i < components; i++) {
+      out[i] = math::max(out[i], 0.0f);
+      if constexpr (std::is_same_v<T, uchar>) {
+        out[i] = math::min(out[i], 255.0f);

@@ -387,3 +397,2 @@
     }
-    else if (filter == IMB_FILTER_BICUBIC) {
-      transform_scanlines_filter<IMB_FILTER_BICUBIC>(ctx, y_range);
+    else if (filter == IMB_FILTER_CUBIC_BSPLINE) {