LibVideo/VP9: Specify more units in Parser::residual()

Previously, the variables were named similarly to the names in spec
which aren't very human-readable. This adds some utility functions for
dimensional unit conversions and names the variables in residual()
based on their units.

References to 4x4 blocks were also renamed to call them sub-blocks
instead, since unit conversion functions would not be able to begin
with "4x4_blocks".

Userland/Libraries/LibVideo/VP9/Utilities.h

@@ -8,6 +8,9 @@
 #pragma once
 
 #include <AK/Types.h>
+#include <LibGfx/Size.h>
+
+#include "LookupTables.h"
 
 namespace Video::VP9 {
 
@@ -42,4 +45,50 @@ inline T brev(C bit_count, T value)
     return result;
 }
 
+inline Gfx::Size<u8> block_size_to_sub_blocks(BlockSubsize size)
+{
+    return Gfx::Size<u8>(num_4x4_blocks_wide_lookup[size], num_4x4_blocks_high_lookup[size]);
+}
+
+template<Integral T>
+inline T blocks_to_sub_blocks(T blocks)
+{
+    return blocks << 1;
+}
+
+template<Integral T>
+inline T sub_blocks_to_blocks(T sub_blocks)
+{
+    return sub_blocks >> 1;
+}
+
+template<Integral T>
+inline T sub_blocks_to_pixels(T sub_blocks)
+{
+    return sub_blocks << 2;
+}
+
+template<Integral T>
+inline T pixels_to_sub_blocks(T pixels)
+{
+    return pixels >> 2;
+}
+
+template<Integral T>
+inline T blocks_to_pixels(T blocks)
+{
+    return sub_blocks_to_pixels(blocks_to_sub_blocks(blocks));
+}
+
+template<Integral T>
+inline T pixels_to_blocks(T pixels)
+{
+    return sub_blocks_to_blocks(pixels_to_sub_blocks(pixels));
+}
+
+inline u8 transform_size_to_sub_blocks(TXSize transform_size)
+{
+    return 1 << transform_size;
+}
+
 }