Convert TiledColor To Struct

[7H3LaughingMan]

Converts TiledColor to a struct similar to how Color is defined in System.Drawing and other libraries. The actual value is a 32-bit unsigned integer with each octet representing a different component. Also defines several standard static colors that can be used.

These changes does manage to reduce the allocated memory and increases performance by a smidge.

[7H3LaughingMan]

BenchmarkDotNet v0.13.12, Windows 11 (10.0.26100.3775)
Intel Core i5-14500, 1 CPU, 20 logical and 14 physical cores
.NET SDK 9.0.203
  [Host]     : .NET 8.0.15 (8.0.1525.16413), X64 RyuJIT AVX2
  DefaultJob : .NET 8.0.15 (8.0.1525.16413), X64 RyuJIT AVX2

Before Changes

Method	Categories	Mean	Median	Ratio	Gen0	Gen1	Allocated	Alloc Ratio
DotTiled	MapFromInMemoryTmjString	4.953 μs	4.937 μs	1.00	0.4730	-	5.81 KB	1.00
TiledLib	MapFromInMemoryTmjString	6.311 μs	6.197 μs	1.30	0.7401	0.0153	9.07 KB	1.56
DotTiled	MapFromInMemoryTmxString	3.129 μs	3.116 μs	1.00	1.3580	0.0610	16.72 KB	1.00
TiledLib	MapFromInMemoryTmxString	5.533 μs	5.549 μs	1.77	1.8921	0.1221	23.31 KB	1.39
TiledCSPlus	MapFromInMemoryTmxString	6.857 μs	6.819 μs	2.19	2.6855	0.1221	33.23 KB	1.99

After Changes

Method	Categories	Mean	Median	Ratio	Gen0	Gen1	Allocated	Alloc Ratio
DotTiled	MapFromInMemoryTmjString	4.428 μs	4.419 μs	1.00	0.4425	-	5.51 KB	1.00
TiledLib	MapFromInMemoryTmjString	6.252 μs	6.224 μs	1.41	0.7401	0.0153	9.07 KB	1.65
DotTiled	MapFromInMemoryTmxString	3.042 μs	3.036 μs	1.00	1.3390	0.0610	16.41 KB	1.00
TiledLib	MapFromInMemoryTmxString	5.801 μs	5.710 μs	2.00	1.8921	0.1221	23.31 KB	1.42
TiledCSPlus	MapFromInMemoryTmxString	6.755 μs	6.684 μs	2.23	2.6855	0.1831	33.16 KB	2.02

[7H3LaughingMan]

I managed to squeeze out a little more performance by using StructLayout and FieldOffset, this way TiledColor is still the size of a uint but there is no need to constantly do bitwise operations to unpack the data.