`maintainVisibleContentPosition` by default is true

[TMaszko]

In types.ts you can find the js doc that says that this property by default is set to false which is not true atm.
Link: https://github.com/LegendApp/legend-list/blob/main/src/types.ts#L191
Actual behaviour: https://github.com/LegendApp/legend-list/blob/main/src/components/LegendList.tsx#L126

More than happy to fix that with quick PR ;)

[TMaszko]

Waiting for the #304 to be merged ;)