[MM-15831] Improve system for storing status of available plug… (#11185)

* Move State property from activePlugin to PluginHealthStatus. env.activePlugins is now reserved for healthy running plugins.

* Add comments for function declarations

* Combine activePlugins and pluginHealthStatuses into a common structure, registeredPlugins

* Add check to see if plugin is active before deactivating it

* Make `Deactivate` set plugin status

* Add comment explaining the `registeredPlugins` map
* Give responsibility to set plugin disabled status upon deactivation back to `env.Deactivate`

* check if plugin needs to be deactivated before setting status

app/plugin_install.go

@@ -130,6 +130,7 @@ func (a *App) removePlugin(id string) *model.AppError {
 	}
 
 	pluginsEnvironment.Deactivate(id)
+	pluginsEnvironment.RemovePlugin(id)
 	a.UnregisterPluginCommands(id)
 
 	err = os.RemoveAll(pluginPath)