Move bar transform functions to bar helpers

[archmoj]

Before addressing #4247
this PR remove bar transform functions namely toMoveInsideBar & toMoveOutsideBar from bar/plot to bar/helpers as those function are required by traces e.g. treemap.
This can also help make bar plot code (which used by histogram, funnel and waterfall) more compact.

@plotly/plotly_js

[etpinard]

I'm not sure I approve. helpers.js files are usually kept from utilities that are used across different methods in a given trace module.

For example, castOption for pies

plotly.js/src/traces/pie/helpers.js

Lines 37 to 40 in dbf02f1

	exports.castOption = function castOption(item, indices) {
	if(Array.isArray(item)) return exports.getFirstFilled(item, indices);
	else if(item) return item;
	};

is called in plot.js and style_one.js

plotly.js/src/traces/pie/plot.js

Line 79 in dbf02f1

var pull = +helpers.castOption(trace.pull, pt.pts) || 0;

plotly.js/src/traces/pie/style_one.js

Lines 16 to 17 in dbf02f1

	var lineColor = castOption(line.color, pt.pts) || Color.defaultLine;
	var lineWidth = castOption(line.width, pt.pts) || 0;

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So, I don't see anything wrong with keeping all bar "plotting" subroutines in bar/plot.js. I don't see anything wrong with having treemap require bar/plot.js either. Moving stuff around simply to make things more compact (which is subjective, by the way) is usually a waste of time.

[archmoj]

I see the point that helpers is not the best place for putting these functions.
So maybe we should put them in a separate file (or leave them where they are).
By the way here is a comment from treemap PR which is quite related:
#4185 (comment)

[etpinard]

So maybe we should put them in a separate file (or leave them where they are).

I vote for leaving them in bar/plot.js.