Unity/C++: Significant re-factoring of Unity header management (see description)

Extract resource handling to UnityResource
Add API header resource helpers
Fix UnityVersion ToString() when Min == Max
Replace fixed list of Il2Cpp header reserved names with parsed names from actual selected headers (solves TypeInfo/MemberInfo problems in 5.3.0-5.3.4 (metadata v16-20))
Use CppDeclarationGenerator when initializing CppTypeCollection to ensure all Il2Cpp header symbols are reserved
Process API headers in CppTypeCollection.FromUnityHeaders
Move #define IS_32BIT handling to UnityHeaders
Update tests

Il2CppInspector.Common/Cpp/UnityHeaders/UnityVersion.cs

@@ -6,7 +6,6 @@
 */
 
 using System;
-using System.Globalization;
 using System.Linq;
 using System.Text.RegularExpressions;
 
@@ -181,7 +180,7 @@ namespace Il2CppInspector.Cpp.UnityHeaders
             var res = $"{Min}";
             if (Max == null)
                 res += "+";
-            else if (Max != Min)
+            else if (!Max.Equals(Min))
                 res += $" - {Max}";
             return res;
         }