Add modebar button for toggling ternary spikelines

[Lexachoc]

Follow-up to #8041.

Similar to the Cartesian spikeline button (toggleSpikelines), this adds a toggleTernarySpikelines button to toggle the ternary spikelines implemented in #8041.

I think this could be very useful.

IMHO, I find the current toggleSpikelines behavior a bit confusing. When I first tried the button, I expected a "toggle" to simply control the visibility of the spikelines, ON or OFF.

That is why toggleTernarySpikelines is designed this way: it hides the current ternary spikelines when turned off and restores their previous visibility states when turned back on.

Reproduce with devtools

Open:

http://localhost:3000/devtools/test_dashboard/index.html

Then run in the console:

Plotly.newPlot(gd, [{
                    type: 'scatterternary',
                    subplot: 'ternary',
                    a: [1],
                    b: [2],
                    c: [3]
                }, {
                    type: 'scatterternary',
                    subplot: 'ternary2',
                    a: [2],
                    b: [3],
                    c: [1]
                }], {
                    ternary: {
                        domain: {x: [0, 0.45]},
                        aaxis: {showspikes: true},
                        baxis: {showspikes: false},
                        caxis: {showspikes: true}
                    },
                    ternary2: {
                        domain: {x: [0.55, 1]},
                        aaxis: {showspikes: false},
                        baxis: {showspikes: true},
                        caxis: {showspikes: false}
                    }
                }, {
                    modeBarButtonsToAdd: ['toggleTernarySpikelines']
                })

Screenshots

Note

While implementing this, I found a bug #8129, where modebar toggle buttons do not use the correct active icon color on initial render. A fix has been submitted in #8130.

Additional

Docs may also need to be updated to list toggleTernarySpikelines on https://plotly.com/javascript/configuration-options/, https://plotly.com/python/configuration-options/, and possibly other related pages.