Fix toggleHover and resetViews modebar buttons for some partial bundle + graph setups

[etpinard]

fix #4164 - by adding fallbacks to fullLayout._subplots[k] entries in modebar buttons handlers called on graphs with different subplot arrangements that may or may not be part of one's partial or custom bundle.

The reason why some fullLayout._subplots[k] are empty in partial bundles is due to this routine here:

plotly.js/src/plots/plots.js

Lines 584 to 624 in 9b5f089

	/**
	* Make a container for collecting subplots we need to display.
	*
	* Finds all subplot types we need to enumerate once and caches it,
	* but makes a new output object each time.
	* Single-trace subplots (which have no `id`) such as pie, table, etc
	* do not need to be collected because we just draw all visible traces.
	*/
	function emptySubplotLists() {
	var collectableSubplotTypes = Registry.collectableSubplotTypes;
	var out = {};
	var i, j;
	if(!collectableSubplotTypes) {
	collectableSubplotTypes = [];
	var subplotsRegistry = Registry.subplotsRegistry;
	for(var subplotType in subplotsRegistry) {
	var subplotModule = subplotsRegistry[subplotType];
	var subplotAttr = subplotModule.attr;
	if(subplotAttr) {
	collectableSubplotTypes.push(subplotType);
	// special case, currently just for cartesian:
	// we need to enumerate axes, not just subplots
	if(Array.isArray(subplotAttr)) {
	for(j = 0; j < subplotAttr.length; j++) {
	Lib.pushUnique(collectableSubplotTypes, subplotAttr[j]);
	}
	}
	}
	}
	}
	for(i = 0; i < collectableSubplotTypes.length; i++) {
	out[collectableSubplotTypes[i]] = [];
	}
	return out;
	}

which loops over the registered base-plot modules - which is a subset of all the available base-plot modules.

cc @plotly/plotly_js - we don't publish partial bundles on CI, so I can't show you a before/after from #4164 (comment) - I hope you'll find the fix trivial enough to not mind. Please let me know if that's not case.

[archmoj]

@etpinard Thanks for the fix and adding tests.
💃