LibVideo/VP9: Finish implementing block decoding (6.4.4)

Though technically block decoding calls into some other incomplete
methods, so it isn't functionally complete yet. However, we are
very close to being done with the 6.4.X sections :)

Userland/Libraries/LibVideo/VP9/Enums.h

@@ -32,7 +32,7 @@ enum ColorRange {
     FullSwing
 };
 
-enum InterpolationFilter {
+enum InterpolationFilter : u8 {
     EightTap = 0,
     EightTapSmooth = 1,
     EightTapSharp = 2,
@@ -40,7 +40,7 @@ enum InterpolationFilter {
     Switchable = 4
 };
 
-enum ReferenceFrame {
+enum ReferenceFrame : u8 {
     // 0 is both INTRA_FRAME and NONE because the value's meaning changes depending on which index they're in on the ref_frame array
     None = 0,
     IntraFrame = 0,
@@ -49,7 +49,7 @@ enum ReferenceFrame {
     AltRefFrame = 3,
 };
 
-enum TXMode {
+enum TXMode : u8 {
     Only_4x4 = 0,
     Allow_8x8 = 1,
     Allow_16x16 = 2,
@@ -57,14 +57,14 @@ enum TXMode {
     TXModeSelect = 4,
 };
 
-enum TXSize {
+enum TXSize : u8 {
     TX_4x4 = 0,
     TX_8x8 = 1,
     TX_16x16 = 2,
     TX_32x32 = 3,
 };
 
-enum ReferenceMode {
+enum ReferenceMode : u8 {
     SingleReference = 0,
     CompoundReference = 1,
     ReferenceModeSelect = 2,