runtime: record all sampled mutex profile events

The block and mutex profiles have slightly different behaviors when a
sampled event has a negative (or zero) duration. The block profile
enforces a minimum duration for each event of "1" in the cputicks unit.
It does so by clamping the duration to 1 if it was originally reported
as being smaller. The mutex profile for app-level contention enforces a
minimum duration of 0 in a similar way: by reporting any negative values
as 0 instead.

The mutex profile for runtime-internal contention had a different
behavior: to enforce a minimum event duration of "1" by dropping any
non-conforming samples.

Stop dropping samples, and use the same minimum (0) that's in place for
the other mutex profile events.

Fixes #64253
Fixes #68453
Fixes #68781

Change-Id: I4c5d23a2675501226eef5b9bc1ada2efc1a55b9e
Reviewed-on: https://go-review.googlesource.com/c/go/+/604355
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Mauri de Souza Meneguzzo <mauri870@gmail.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Auto-Submit: Rhys Hiltner <rhys.hiltner@gmail.com>

src/runtime/mprof.go

@@ -722,8 +722,8 @@ type mLockProfile struct {
 }
 
 func (prof *mLockProfile) recordLock(cycles int64, l *mutex) {
-	if cycles <= 0 {
-		return
+	if cycles < 0 {
+		cycles = 0
 	}
 
 	if prof.disabled {