10.1.x: USDT: normalize names for STATE_ENTER

[moonchen]

Backport of #13346.

STATE_ENTER passed &HttpSM::<state> straight through as the USDT probe
name, so probes were emitted as e.g. &HttpSM::state_read_client_request_header.
The & and :: characters are illegal in USDT probe names: bpftrace and perf
treat : as the provider/name field separator and reject &, so these probes
could not be attached by name.

Pass the bare handler name from each call site and add the prefix in the
macro, producing valid names like state_enter_state_read_client_request_header
that share a common state_enter_* wildcard. Also fixes a &HttpSM : typo
that had collapsed one probe to a bare &HttpSM, and a call site that passed
the wrong label (tunnel_handler_plugin_client from tunnel_handler_plugin_agent)
so the probe name matches its handler.

Did not cherry-pick cleanly:

• state_http_server_open conflicted with the exponential-backoff retry
  logic from Retry Connect with Exponential Backoff #12397, which isn't in 10.1.x; resolved by keeping 10.1.x's
  version of that function.
• Two call sites that 10.1.x still carries but master no longer has
  (state_pre_resolve, state_mark_os_down) also needed converting to the
  new macro syntax, or the file wouldn't compile.

Verified traffic_server builds clean on 10.1.x with this applied.

[moonchen]

@cmcfarlen