updateTextScale method
Implementation
void updateTextScale(ScaleUpdateDetails details) {
double newScaleFactor = state.baseScaleFactor.value * details.scale;
if (newScaleFactor < 1.0) {
newScaleFactor = 1.0;
} else if (newScaleFactor < 4) {
state.scaleFactor.value = newScaleFactor;
}
update(['_pageViewBuild']);
}