Convert DefaultPlugin to a plugin group

[waynemwashuma]

Objective

Refactor DefaultPlugin to use the PluginGroup instead of registering plugins manually through the App instance.

Solution

DefaultPlugin has been converted into a PluginGroup.

Showcase

Applications can now load all core plugins through a single plugin group. This enables users to add, remove or modify default plugins before registration.

const defaults = new DefaultPlugin()

defaults.remove(typeid(TimePlugin))
defaults.add(new TimePlugin())

app.registerPlugin(default)

Migration guide

No changes are required for most applications.

Checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.