hmp: Add 'one-insn-per-tb' command equivalent to 'singlestep'

The 'singlestep' HMP command is confusing, because it doesn't
actually have anything to do with single-stepping the CPU.  What it
does do is force TCG emulation to put one guest instruction in each
TB, which can be useful in some situations.

Create a new HMP command  'one-insn-per-tb', so we can document that
'singlestep' is just a deprecated synonym for it, and eventually
perhaps drop it.

We aren't obliged to do deprecate-and-drop for HMP commands,
but it's easy enough to do so, so we do.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20230417164041.684562-9-peter.maydell@linaro.org

tests/qtest/test-hmp.c

@@ -56,6 +56,7 @@ static const char *hmp_cmds[] = {
     "o /w 0 0x1234",
     "object_add memory-backend-ram,id=mem1,size=256M",
     "object_del mem1",
+    "one-insn-per-tb on",
     "pmemsave 0 4096 \"/dev/null\"",
     "p $pc + 8",
     "qom-list /",