Fix slow scattergl hover

[emilykl]

Closes #5927, closes #5790

Fixes performance issue where scattergl plots were performing an expensive operation searching all points on hover by default.

The impact is severe for plots with many points (say, >100k; see linked issues for details).

[Lexachoc]

Hi, I may submit PRs for #7972 (spikelines for ternary plots) and #7058 (new scatterternarygl trace) recently.

Both may overlap with the hover/spikeline logic changed here, especially this line (depending on my implementations):

plotly.js/src/components/fx/hover.js

Line 676 in 0a69fa1

if (hasCartesian && spikedistance !== 0 && canSpikeToClosest(pointData)) {

Just wanted to flag the connection so I can account for these changes.

[emilykl]

Closing in favor of #8052

[emilykl]

Thanks @Lexachoc for the heads-up!

I've posted a more finalized version of this PR in #8052, feel free to take a look. If the PR is accepted, you could incorporate the changes into #8041.