Consider a different return type for `Symbol.Aliases`

[jonsequitur]

    public abstract class IdentifierSymbol : Symbol, ICompletionSource 
    {
        // "Is this the right return type?"
        public IReadOnlyCollection<string> Aliases { get; }

Related: #1859

[KalleOlaviNiemitalo]

I totally expected option.Aliases[0] to work, but it requires Enumerable.First instead.

In System.CommandLine 2.0.0-beta4.22272.1, the collection is a HashSet<string> and thus does not preserve order. However, I feel it might be better to preserve order here and instead make the parser build a Dictionary<string, Symbol>.

command-line-api/src/System.CommandLine/IdentifierSymbol.cs

Line 14 in 209b724

private protected readonly HashSet<string> _aliases = new(StringComparer.Ordinal);

command-line-api/src/System.CommandLine/IdentifierSymbol.cs

Lines 37 to 40 in 209b724

	/// <summary>
	/// Gets the set of strings that can be used on the command line to specify the symbol.
	/// </summary>
	public IReadOnlyCollection<string> Aliases => _aliases;

[KalleOlaviNiemitalo]

Since #2073, it is ICollection<string> Aliases { get; }, backed by internal class AliasSet:

command-line-api/src/System.CommandLine/Command.cs

Line 91 in fe66356

public ICollection<string> Aliases => _aliases ??= new();

command-line-api/src/System.CommandLine/Option.cs

Line 105 in fe66356

public ICollection<string> Aliases => _aliases ??= new();

command-line-api/src/System.CommandLine/AliasSet.cs

Line 7 in fe66356

internal sealed class AliasSet : ICollection<string>

(Argument and Directive do not have an Aliases property. It would not be useful for Argument, but could be for Directive.)