Fix S3900 FP: Don't raise if parameter is captured

[martin-strecker-sonarsource]

Description

S3900 is falsely raised when the parameter is captured:

    public string InsideLambda(string s)
    {
        if (s == null)
        {
            return null;
        }

        Func<string> someFunc = () => s.ToString();

        return s.ToString(); // Noncompliant FP: S3900 "Refactor this method to add a validation of parameter 's'"
    }

Root cause

When we enter the block after the return, s has the NotNull constraint as expected. s is also in the captured list of LiveVariableAnalysisBase. Therefore it is not included in the LiveOut list:

        /// <summary>
        /// LiveOut variables are alive when exiting block. They are read in any of it's successors.
        /// </summary>
        public IReadOnlyCollection<ISymbol> LiveOut(TBlock block) =>
            blockLiveOut[block].Except(captured).ToImmutableArray();

And that is why it gets removed in ProcessBranchState:

sonar-dotnet/analyzers/src/SonarAnalyzer.Common/SymbolicExecution/Roslyn/RoslynSymbolicExecution.cs

Lines 165 to 167 in 0d3caf3

	var liveVariables = lva.LiveOut(branch.Source).ToHashSet();
	return state.RemoveSymbols(x => lva.IsLocal(x) && (x is ILocalSymbol or IParameterSymbol { RefKind: RefKind.None }) && !liveVariables.Contains(x))
	.ResetOperations();