Tracking issue for Error changes

[KathleenDollard]

For parsing

• [ ] Approve Error proposal
• [ ] Change ParseError name to CliError
• [ ] Create CliError and CliDiagnosticDescriptor
• [ ] Replace all error creation with 'CliError'
• [ ] Comment out code for argument required, option and command (*)
• [ ] Comment out ArgumentArity.Validate and its call in ArgumentResult and CommandResult after checking the proposal's explanation of maximum arity and token limit reached (**)
• [ ] Change SymbolTree.AddError to take a CliError and associated fixes
• [ ] Collect SymbolTree errors into ParseResult.Errors
• [ ] Update existing tests to use CliError
• [ ] Add any additional tests deemed necessary

(*) This is a validation check that does not need to affect further parsing. In its current form, it also blocks making ParseResult sparse.

(**) See Arity section of Error proposal

For ErrorReporting subsystem

TBD