LibVideo: Implement VP9 intra-predicted frame decoding

The first keyframe of the test video can be decoded with these changes.

Raw memory allocations in the Parser have been replaced with Vector or
Array to avoid memory leaks and OOBs.

Userland/Libraries/LibVideo/VP9/Utilities.h

@@ -11,7 +11,35 @@
 
 namespace Video::VP9 {
 
-u8 clip_3(u8 x, u8 y, u8 z);
-u8 round_2(u8 x, u8 n);
+// FIXME: Once everything is working, replace this with plain clamp
+// since parameter order is different
+template<typename T>
+T clip_3(T x, T y, T z)
+{
+    return clamp(z, x, y);
+}
+
+template<typename T>
+u16 clip_1(u8 bit_depth, T x)
+{
+    if (x < 0) {
+        return 0u;
+    }
+    const T max = (1u << bit_depth) - 1u;
+    if (x > max)
+        return max;
+    return x;
+}
+
+template<typename T, typename C>
+inline T brev(C bit_count, T value)
+{
+    T result = 0;
+    for (C i = 0; i < bit_count; i++) {
+        auto bit = (value >> i) & 1;
+        result |= bit << (bit_count - 1 - i);
+    }
+    return result;
+}
 
 }