Offer textScaler

[jakobleck]

With a recent (well, not that recent...) Flutter update textScaleFactor has been deprecated and replaced by textScaler. This change appears in the Text widget and thus should also be implemented in Linkify.

[bbjay]

I use this as a workaround to support system text scaling:

textScaleFactor: MediaQuery.textScalerOf(context).scale(1),