Add AvoidReservedWordsAsFunctionNames Rule

[liamjpeters]

PR Summary

Adds a new rule that warns when reserved words are used as function names.

function function {}

function if {
    function else {}
}

function global:try {}

function private:catch {}

Fixes #2099

I wrote a blog post about putting this together 😀

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  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header
• Make sure you've added a new test if existing tests do not effectively test the code changed and/or updated documentation
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[liamjpeters]

Just as a note...

I did attempt to use reflection rather than a hard-coded list of keywords. The keyword list is in the Tokenizer.

public static HashSet<string> GetReservedWordsFromTokenizer()
{
    // Get the assembly containing Tokenizer
    var asm = typeof(Token).Assembly;

    // Get the internal Tokenizer type
    var tokenizerType = asm.GetType("System.Management.Automation.Language.Tokenizer");

    // Get the private static readonly field s_keywordTokenKind
    var field = tokenizerType.GetField("s_keywordTokenKind", BindingFlags.NonPublic | BindingFlags.Static);

    // Get the TokenKind[] value
    var tokenKinds = field.GetValue(null) as Array;

    var reservedWords = new HashSet<string>(
        tokenKinds.Cast<Enum>().Select(tk => tk.ToString()),
        StringComparer.OrdinalIgnoreCase
    );

    return reservedWords;
}

With similar on the PowerShell side for the tests.

This worked fine in PS7 but I can't seem to get it to work in PS5.1 - I can't access the s_keywordTokenKind or s_keywordText field.