Fix mathjax placement in ternary aaxis titles

[etpinard]

fixes #3455 -- cc @plotly/plotly_js

I was really hoping to get rid of this hacky block

plotly.js/src/lib/svg_text_utils.js

Lines 127 to 142 in 84e24aa

	if(svgClass[0] === 'y') {
	mathjaxGroup.attr({
	transform: 'rotate(' + [-90, +_context.attr('x'), +_context.attr('y')] +
	') translate(' + [-newSvgW / 2, dy - newSvgH / 2] + ')'
	});
	newSvg.attr({x: +_context.attr('x'), y: +_context.attr('y')});
	}
	else if(svgClass[0] === 'l') {
	newSvg.attr({x: _context.attr('x'), y: dy - (newSvgH / 2)});
	}
	else if(svgClass[0] === 'a') {
	newSvg.attr({x: 0, y: dy});
	}
	else {
	newSvg.attr({x: newX, y: (+_context.attr('y') + dy - newSvgH / 2)});
	}

entirely, but since our MathJax test coverage is lackluster, I chose the safe road.

[etpinard]

@antoinerg or @archmoj could one of you review this thing at some point today?

Thank you!

[archmoj]

Could we use

if(svgClass === 'atitle') {

here?

[etpinard]

Why would that be better?

[archmoj]

I was wondering of an edge case where 'atitle' appears in other position in the text.
Though I was not able find any word containing those letters in order!
Anyway could we use this condition instead to test if atitle only occurs at the start of the string?

else if(svgClass[0] === 'a' && svgClass.indexOf('atitle') !== 0) {

[etpinard]

Ok. Done in -> c7878b3

[archmoj]

Thanks @etpinard for fixing this bug.
💃 when the tests were passed.