[google_maps_flutter] fix crash and remove listeners

[cyanglaz]

Description

Map plugins crashes when exiting app while using the FragmentActivity.
We are calling MapView.onDestroy at an inappropriate location which caused sone undefined behavior. MapView.onDestroy should only be called in the corresponding onDestroy method in from the activity or fragment. According to https://developers.google.com/android/reference/com/google/android/gms/maps/MapView#onDestroy%28%29 "You must call this method from the parent Activity/Fragment's corresponding method."

Also added some house keeping code to remove all the listeners when disposing.

Related Issues

Fixes flutter/flutter#55406

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[xster]

LGTM, thanks

[cyanglaz]

the crash seems to be something new related to google map sdk
https://stackoverflow.com/questions/61397027/androidruntime-fatal-exception-androidmapsapi-zoomtablemanager-java-lang-arra
b/154855417

[xster]

ummm do we need a specific maps version constraint in our gradle in the meantime for our plugin?

[cyanglaz]

@xster It seems to pass now (at least for my other gmap PR) Will see how this one goes.

[xster]

Still LGTM