Add GetLeftSideOfDot from Roslyn

[Tim-Pohlmann]

GetLeftSideOfDot would be very useful in a lot of places and should be brought over to our code base.

Example use case:

sonar-dotnet/analyzers/src/SonarAnalyzer.CSharp/Rules/RedundantCast.cs

Lines 146 to 154 in 95278ed

	ExpressionSyntax CollectionExpression() =>
	methodSymbol.MethodKind is MethodKind.ReducedExtension
	? invocation.Expression switch
	{
	MemberAccessExpressionSyntax { Expression: { } memberAccessExpression } => memberAccessExpression,
	MemberBindingExpressionSyntax => invocation.GetParentConditionalAccessExpression().Expression,
	_ => null
	}
	: invocation.ArgumentList.Arguments.FirstOrDefault()?.Expression;