Fix *all* OS / browser-dependent scattergl text oddities

[etpinard]

Follow-up of #2737

scattergl text works well on @dy's Windows laptop in both Chrome, FF and IE11 (please correct me if I'm wrong @dy), but features a few oddities in FF on MacOS and Ubuntu 16.04 and Safari.

Copying @alexcjohnson 's report:

On Mac OS 10.13.5, retina display. For reference here's the SVG text_chart_arrays mock, which AFAICT looks identical on Chrome, FF, and Safari:

But the gl2d version looks bold and blurry (perhaps this is retina-only, related to #2756?), and there are first-load issues in FF (missing some items entirely) and Safari (wrong font).
Here's Chrome:

FF the first render in a given tab is missing some items:

But the second gets them all:

And Safari on first render has the wrong font for "Text G":

but it's fixed on second render:

[etpinard]

bug report from @chriddyp

The latest scattergl text is not rendering for me on Firefox 61.0, MacOS 10.13.4. It renders for me in Chrome.

Chrome:

Firefox:

Firefox Console:

[etpinard]

assigning @dy

[chriddyp]

Another report: https://community.plot.ly/t/scattergl-inconsistently-supports-custom-fonts/29280

[gvwilson]

Hi - this issue has been sitting for a while, so as part of our effort to tidy up our public repositories I'm going to close it. If it's still a concern, we'd be grateful if you could open a new issue (with a short reproducible example if appropriate) so that we can add it to our stack. Cheers - @gvwilson