WebP - Reduce the allocations in lossless encoding

Prerequisites

[x] I have written a descriptive pull-request title
[x] I have verified that there are no overlapping pull-requests open
[x] I have verified that I am following the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules :cop:.
[x] I have provided test coverage for my change (where applicable)

Description

This PR refactors the Vp8LHistogram type to use pooled allocations. It also introduces the concept of a Vp8LHistogramSet type to allow allocating a single buffer for a collection.

Benchmark indicates a 20ms speedup for lossless encoding while using less than half the original allocated memory.

BenchmarkDotNet=v0.13.0, OS=Windows 10.0.22621
11th Gen Intel Core i7-11370H 3.30GHz, 1 CPU, 8 logical and 4 physical cores
.NET SDK=8.0.100-rc.1.23455.8
  [Host]     : .NET 6.0.22 (6.0.2223.42425), X64 RyuJIT
  Job-ZADQXC : .NET 6.0.22 (6.0.2223.42425), X64 RyuJIT

Runtime=.NET 6.0  Arguments=/p:DebugType=portable  IterationCount=3
LaunchCount=1  WarmupCount=3

Main

Method	TestImage	Mean	Error	StdDev	Ratio	RatioSD	Gen 0	Gen 1	Gen 2	Allocated
'Magick Webp Lossy'	Png/Bike.png	22.30 ms	5.533 ms	0.303 ms	0.14	0.00	-	-	-	68 KB
'ImageSharp Webp Lossy'	Png/Bike.png	74.82 ms	2.291 ms	0.126 ms	0.46	0.00	2428.5714	142.8571	-	15,187 KB
'Magick Webp Lossless'	Png/Bike.png	161.16 ms	22.093 ms	1.211 ms	1.00	0.00	-	-	-	518 KB
'ImageSharp Webp Lossless'	Png/Bike.png	249.44 ms	58.373 ms	3.200 ms	1.55	0.02	8000.0000	4000.0000	2000.0000	46,532 KB

Method	TestImage	Mean	Error	StdDev	Ratio	RatioSD	Gen 0	Gen 1	Gen 2	Allocated
'Magick Webp Lossy'	Png/Bike.png	22.20 ms	5.392 ms	0.296 ms	0.13	0.00	-	-	-	68 KB
'ImageSharp Webp Lossy'	Png/Bike.png	76.90 ms	61.754 ms	3.385 ms	0.46	0.01	2428.5714	142.8571	-	15,187 KB
'Magick Webp Lossless'	Png/Bike.png	165.44 ms	85.798 ms	4.703 ms	1.00	0.00	-	-	-	518 KB
'ImageSharp Webp Lossless'	Png/Bike.png	228.72 ms	40.127 ms	2.199 ms	1.38	0.05	3000.0000	2000.0000	2000.0000	20,623 KB

SixLabors / ImageSharp

WebP - Reduce the allocations in lossless encoding #2546

Prerequisites

Description