refactor(addon): cleanup constructors

[yousinix]

Lift the setting parameters to the addon constuctor itself. This helps making the addon API more readable, and much simpler.

Before

TextScaleAddon(
  setting: TextScaleSetting(
    textScales: [
      1.0,
      2.0,
    ],
    activeTextScale: 1.0,
  ),
),

After

TextScaleAddon(
  scales: [1.0, 2.0],
  initialScale: 2.0
);

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[jenshor]

In general, the developer has to be able to specify the default "setting" on startup.