Force plugin uninstallation

[brandonkelly]

This PR adds a $force arg to craft\services\Plugins::uninstallPlugin(), which forces the plugin to be removed from the plugins table and project config, even if:

• it’s disabled
• it’s enabled but its uninstall() method returns false
• its files aren’t present (Composer-uninstalled already)

The plugin/uninstall console command also now has a --force flag, which will pass true to $force.

> php craft plugin/uninstall smart-map
*** uninstalling smart-map
*** failed to uninstall smart-map: Uninstalling disabled plugins is not allowed.
Try again with --force.

> php craft plugin/uninstall smart-map --force
*** uninstalling smart-map
*** uninstalled smart-map successfully (time: 0.215s)

To avoid unexpected PHP errors, if plugin uninstallation is forced for a disabled plugin, its uninstall() method will not be called.