Completion support

[sergei-dyshel]

Is System.CommandLine's completion support also exposed by this library? Specifically 2 AIs:

• Support .CommandLineBuilder UseSuggestDirective (description) for registering tool with dotnet-suggest..
• Generating list of completions at runtime, as described here https://learn.microsoft.com/en-us/dotnet/standard/commandline/tab-completion#get-tab-completion-values-at-run-time

[calacayir]

[suggest] directive is enabled by default and can be disabled with CliSettings.EnableSuggestDirective.

dotnet [suggest] buil

build
build-server
msbuild

For completions, we need to add property to CliArgument and CliOption attributes. I will let you know.