perf(track): reduce webgl memory usage

[etowahadams]

Fix #
Toward #

Interacting with a visualization causes webgl memory to skyrocket. I use about:memory in Firefox to check memory usage.

This was because Graphics objects were not being destroyed between draw calls, causing an accumulation of Graphics objects. With this fix, webgl textures memory only gets up to 10-15 MB.

Change List

• Destroy the Graphics objects in pBorder before redrawing

Checklist

• Ensure the PR works with all demos on the online editor
• Unit tests added or updated
• Examples added or updated
• Documentation updated (e.g., added API functions)
• Screenshots for visual changes (e.g., new encoding support or UI change on Editor)

[sehilyi]

Maybe this was not the intended change?

[etowahadams]

Good catch!