top(1): Add missing display messages when toggling modes

[james.wright_digital-chaos.com]

Summary

Added missing display messaging when toggling by the following;

m : "Displaying IO stats" / "Displaying CPU stats"
S: "Displaying system processes" / "Not displaying system processes"
a: "Displaying process args" / "Not displaying process args"

Bugzilla;
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=233667

Test Plan

1. Run patched top
2. Verify display of relevant message when toggling on/off;

m : "Displaying IO stats" / "Displaying CPU stats"
S: "Displaying system processes" / "Not displaying system processes"
a: "Displaying process args" / "Not displaying process args"

[markj]

Seems reasonable to me.

[markj]

Sorry, I meant to commit this. That said, after looking at top.c I have a couple of nits: is there any reason to abbreviate "args" and "stats"? We don't seem to do that in general (e.g., "processes" instead of "procs"), and other messages spell out "statistics." Second, other messages end with a period, so we should do that here too.

[james.wright_digital-chaos.com]

Updated with regards to feedback suggested by markj

Was unsure about ending the messages with a period as there is already a mixture in the existing code. I have included the period as suggested in these new messages and removed any abbreviations.