Fix modebar not recreated when makePlotFramework called

[Yook74]

Fixes #4974

If makePlotFramework was called when updating an existing plot, the modebar div would be cleared, but gd._fullLayout._modeBar which tracks the modebar's state would not be changed. If gd._fullLayout._modeBar was not changed, this conditional
would update the modebar instead of creating it. Updating the modebar in this context does not work though, since the modebar div has been cleared.

My extremely simple fix is to clear the modebar's state stored in gd._fullLayout._modeBar when clearing the modebar div in makePlotFramework.

[alexcjohnson]

Thanks @Yook74! this indeed looks like exactly the right fix 🎉

The only thing we need now is a test - ideally this would be something like the modebar styling tests - createGraphDiv before, destroyGraphDiv after, and the test itself would be

Plotly.plot(gd, data, layout).then(function() {
    // test that the initial modebar is present
    var modeBar = gd._fullLayout._modeBar;
    expect(countGroups(modeBar)).toEqual(6); // whatever buttons should be there

    // some modification that would have broken the modebar before your fix:
    // react, restyle, click a button... whatever's easiest
    return Plotly.react(gd, newData, newLayout);
}).then(function() {
    // test that the new modebar is present
    var modeBar = gd._fullLayout._modeBar;
    expect(countGroups(modeBar)).toEqual(12); // different (nonzero) number of buttons
})
.catch(failTest)
.then(done)

[Yook74]

I wrote tests to catch the particular problem I was having (#4974).

[archmoj]

I wrote tests to catch the particular problem I was having (#4974).

Thanks for the tests. They pass on my machine. I also re-run the CI tests so that they pass.

[archmoj]

Nicely done. 💃