#3026: Viewers: Scatterplot: label placement improvements

[andrew-golovko-datagrok]

Provide advanced label placement for scatterplot labels:

• Use multiple columns as labels
• Display only labels that have enough free space around, join each with its marker in case the label is too far
• Selecting "Labels" -> "Show Marker Labels", place as many labels as possible by default if "Labels" -> "Show Labels For" property is set as "all' or "filtered"
• Otherwise display all the necessary labels:
  • Simple text or image if there's enough space for each label (it doesn't overlap at least one marker)
  • Display text inside block with an outline and background coior otherwise

[dnillovna]

This issue has been mirrored in Jira: https://reddata.atlassian.net/browse/GROK-16630