IDE0083 looks only for declaration patterns

[Youssef1313]

roslyn/src/Analyzers/CSharp/Analyzers/UsePatternMatching/CSharpUseNotPatternDiagnosticAnalyzer.cs

Lines 64 to 77 in d57cddb

	// Look for the form: !(x is Y y)
	if (!(node is PrefixUnaryExpressionSyntax
	{
	Operand: ParenthesizedExpressionSyntax
	{
	Expression: IsPatternExpressionSyntax
	{
	Pattern: DeclarationPatternSyntax,
	} isPattern,
	},
	} notExpression))
	{
	return;
	}

The above implementation will produce a diagnostic for !(x is Y y) but not for !(x is Y). Both can use is not and should have diagnostic.

[reacheight]

Seems like this analyzer and corresponding code fix should also handle binary is-expressions with types (!(x is string)) and constant is-patterns (!(x is null)). If that's ok I'd like to work on this.