Refactor PackageWatchdog explicit health checks

Improvements:

1. Queuing PackageWatchdog requests to startObserving packages:
When observing packages with the watchdog, we needed to get
the packages supporting explicit health checks so we can decide if a
package should be passing or not. This prevents us from receiving
requests to monitor packages during early boot, before third party
packages are ready. In this change we don't depend on ExtServices to
be up to startObserving, we initially treat all package as failing a
health check and lazily syncRequests to request or cancel explicit
health checks based on the currently observed packages. When we receive
onSupportedPackages, we mark the packages that don't support health
checks as passing.

2. Lazy binding to the explicit health check service:
We were always bound to the explicit health check
service regardless of whether we are expecting requests or not, we need
to be able to bind and unbind dynamically to improve device resource
usage. In this change, we bind as soon as we make a request and are
expecting results, we unbind otherwise.

3. Fixed Races:
There were a couple of potential races that could lead to exceptions
that could bring the system server down, e.g when the service is
transitioning between disconnected and connected state (maybe it
crashed) or when ExtServices is being upated and is down or early
boot requests when third party apps are not ready. This change fixes such.

4. Logging:
We improved the logging wording and order and made it more consistent

Bug: 120598832
Test: Manual tests. Stress tested behavior by killing extservices and
making requests simultaneously

function killproc {
    while true
    do
        local pid=$(adb shell pidof $1)
        if [[ ! -z $pid ]]
        then
            echo $pid
            adb shell kill $pid
        fi
    done;
}

adb install-multi-package -i com.android.shell --enable-rollback \
NetworkStack.apk ModuleMetadataGoogle.apk

Also switched between enabled and disabled states to verify packages
are handled correctly. Will automate these tests in later cl

atest PackageWatchdogTest
Change-Id: Iafaef553e95d107f700109f9a8328950a5e2bf71