Add code hotspots chart to code analytics

What does this MR do?

This MR adds the code hotspots chart for the new Code Analytics feature.

This is behind the code_analytics feature flag introduced in !17618 (merged)

The chart being used in this MR will eventually be replaced by a gitlab-ui component being worked on here gitlab-ui!799 (closed)

Follow-up issue to replace local treemap implementation with gitlab-ui version: #34567 (closed)

Code Analytics plan

The MR adds the chart for the following plan

Screenshots

Desktop

Landing	No project	Chart	Tooltip

Recording

CodeAnalytics

Mobile

Landing	No project	Chart	Tooltip

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Style guides