Handle reverse support in core.scale

[kurkle]

• _configure scales after placing them
• handle ticks.reverse in getPixelForDecimal
• add getDecimalForPixel
• utilize getPixelForDecimal and _configure results in scales
• some of scale.logarithmic.tests were actually targeting linear scale (this took a while to figure out)
• -472 -403 bytes (much of this by moving helpers.log10)

Doing essentially the same thing as #6342, just a bit more abstractly.

Forked fiddle (notice horizontalBar reverse is reversed compared to 6342)

Closes #3306
Closes #6342

[benmccann]

I haven't really reviewed yet. I like the idea that we could handle reverse in core.scale. It seems like some of the scales still know about reverse though? E.g. I would have expected if all the logic is being done in core.scale that this PR would be removing reverse from scale.time

[nagix]

Chart.js/src/core/core.scale.js

Lines 73 to 75 in 97f819d

	lineValue -= scale.isHorizontal() ?
	Math.max(lineValue - scale.left, scale.right - lineValue) :
	Math.max(lineValue - scale.top, scale.bottom - lineValue);

These lines can be replaced with

lineValue -= Math.max(lineValue - scale._start, scale._end - lineValue);

Also,

Chart.js/src/core/core.scale.js

Line 1137 in 97f819d

scaleLabelX = me.left + ((me.right - me.left) / 2); // midpoint of the width

Chart.js/src/core/core.scale.js

Line 1146 in 97f819d

scaleLabelY = me.top + ((me.bottom - me.top) / 2);

can be:

scaleLabelX = me.left + me.width / 2; // midpoint of the width

scaleLabelY = me.top + me.height / 2;

[kurkle]

Updated, all comments should be resolved.

[kurkle]

Added _configure to scale.linearBase and scale.logarithmic. Updated scale.time to be consistent.

[kurkle]

Another update. Added offset support for linear scale to be consistent. Need to add tests for that.

[benmccann]

lgtm. just had one last question