Make defaultTouchedIndicators customizable without local re-implementation

It would be nice if the parameters within defaultTouchedIndicators for LineChart were accessible without re-implementing the whole function. Like indicator dot size, color and etc.

Start by locating LineChart's defaultTouchedIndicators implementation and inspect how its indicator dot size, color, and other parameters are fixed. The work is done when callers can customize those parameters without re-implementing the whole function; the issue does not mention a specific file or test to run.

Written by the indexing model from the issue text.