[AsadIqbal-Dev]

Fixes #510

Running any of the tools with no arguments printed Required command was not provided. and exited with 1, because the root command has subcommands but no action. The System.CommandLine limitation mentioned in the issue (dotnet/command-line-api#653) is gone in the 2.0 API, so the root command can now be given HelpAction.

The change is the same one line in each tool: dotnet-counters, dotnet-trace, dotnet-dump, dotnet-gcdump, dotnet-stack, dotnet-dsrouter and dotnet-sos.

Checked each built tool by hand:

Tool	no arguments	bogus (unknown command)	--version
dotnet-counters	help, exit 0 (was error, exit 1)	error, exit 1	exit 0
dotnet-trace	help, exit 0 (was error, exit 1)	error, exit 1	exit 0
dotnet-dump	help, exit 0 (was error, exit 1)	error, exit 1	exit 0
dotnet-gcdump	help, exit 0 (was error, exit 1)	error, exit 1	exit 0
dotnet-stack	help, exit 0 (was error, exit 1)	error, exit 1	exit 0
dotnet-dsrouter	help, exit 0 (was error, exit 1)	error, exit 1	exit 0
dotnet-sos	help, exit 0 (was error, exit 1)	error, exit 1	exit 0

Unknown commands and other parse errors still fail as before.