PR Checklist:

• I have tested this extensively and it does not break any existing behavior.
• I have added/updated examples and tests for any new behavior.
• If this is a significant change, an issue has already been created where the problem / solution was discussed: [N/A, or add link to issue here]
  

PR Description

Improve cache from circle image on LineChartRenderer
Changed mImageCache from HashMap to WeakHashMap to avoid OOM
Moved DataSetImageCache.init to be inside of fill method. The main idea is check if the color have been changed and update circle if it is true.

Motivation:

I created this PR because I met one use case that I needed to use different colors from dots and changed it dinamically from a "hover" on graph. So I used the method setCircleColors, but when I call drawCircle it doesn’t works because the length of the circle array(drawCircles:777) have not been changed. So, in my use case the size keep the same only the color changed.

Selected:

Unselected: