Switch R2RDump over to the new command line parser (dotnet/coreclr#27440)

Switch R2RDump over to the new command line parser (dotnet/coreclr#27440)

This change modifies R2RDump to use the new
System.CommandLine.Experimental module instead of the obsoleted
System.CommandLine parser we were using before. Apart from general
hygiene w.r.t. using up-to-date components one practical reason
for this switch-over is that the old parser is only available on
the unreliable myget.org nuget feed we plan to drop as part of
our planned repo consolidation.

During debugging of the change I noticed a bug in the implementation
of the "--verbose" option - it shouldn't be setting EntryPoints,
otherwise we actually end up with a super-terse output including
just the entry points. I have anecdotally verified that, after fixing
this in both the "new" and "old" R2RDump both produce identical output.

Thanks

Tomas

Commit migrated from https://github.com/dotnet/coreclr/commit/a0d03272dbe691005d74edff73a36c012d38fa1b