`file` `record` `required` `scoped` should be keywords

[moomiji]

file record required scoped contextual keywords were introduced after C# 8.

v3.4.19 will result in the following errors:

• CS9056: Types and aliases cannot be named 'file'.
• CS8860: Types and aliases should not be named 'record'.
• CS9029: Types and aliases cannot be named 'required'.
• CS9062: Types and aliases cannot be named 'scoped'.

LinqToXsdCore/XObjectsCode/Src/NameMangler.cs

Lines 23 to 35 in fb6d59a

	keywords = new HashSet<string>(StringComparer.Ordinal)
	{
	"abstract", "event", "new", "struct", "as", "explicit", "null", "switch",
	"base", "extern", "object", "this", "bool", "false", "operator", "throw",
	"break", "finally", "out", "true", "byte", "fixed", "override", "try", "case",
	"float", "params", "typeof", "catch", "for", "private", "uint", "char", "foreach",
	"protected", "ulong", "checked", "goto", "public", "unchecked", "class",
	"if", "readonly", "unsafe", "const", "implicit", "ref", "ushort", "continue",
	"in", "return", "using", "decimal", "int", "sbyte", "virtual", "default",
	"interface", "sealed", "volatile", "delegate", "internal", "short", "void",
	"do", "is", "sizeof", "while", "double", "lock", "stackalloc", "else", "long",
	"static", "enum", "namespace", "string", "var"
	};