Fix RCS1216

[jamesHargreaves12]

Currently, if an unsafe local block is located inside a for statement then one of the asserts will fail https://github.com/JosefPihrt/Roslynator/blob/1d035ba7b32fafd9057e3c02f3a903a1493ae212/src/Analyzers/CSharp/Analysis/UnnecessaryUnsafeContextAnalyzer.cs#L248

For example

    class C
    {
        unsafe void M()
        {
            for(int y = 0; y < 10; y ++){
                unsafe void M2() {
                    var x = 1;
                }
            }
        }
    }

To fix this and make the code easier to grok I refactored the 3 distinct methods of walking up the syntax tree checking for unsafe modifiers into a single loop. I also Added a new test suite for the analyzer/code fix of RCS1216 as one currently does not exist.

[josefpihrt]

If you want to simplify the code even more, the method

private static void AnalyzeMemberDeclaration(SyntaxNodeAnalysisContext context)

can include all type declarations and member declarations. Virtually all cases except UnsafeStatement and LocalFunctionStatement.