Update stale documentation for axis titles

[carsonalh]

Updated the documentation for the types on axis labels.

In the corresponding index.esm.d.ts file, put JSDoc descriptions for the properties to match the now-updated documentation.

Closes #9682

[LeeLenaleee]

The links in the docs shouldn't be changed, the reason it's done like this is because from a lot of places in the docs there are links to those places so if the typing changes you only have to adjust it in 1 place.

While looking at the docs and the types it seems that according to the typing the padding can either be a number or on object like so: {top, bottom} while according to the docs it should be either a number, object containing {top, bottom, left, right} or an object containing {x, y}.

If you could confirm if all of those work and update the typefile accordingly it would be nice

[carsonalh]

The links in the docs shouldn't be changed, the reason it's done like this is because from a lot of places in the docs there are links to those places so if the typing changes you only have to adjust it in 1 place.

While looking at the docs and the types it seems that according to the typing the padding can either be a number or on object like so: {top, bottom} while according to the docs it should be either a number, object containing {top, bottom, left, right} or an object containing {x, y}.

If you could confirm if all of those work and update the typefile accordingly it would be nice

The old version of the documentation made it clear that the left and right properties are not implemented, so they weren't in the type file. I tested in version 3.5.1 and the {x, y} format for padding doesn't seem to work either, so I've left the type unchanged, in both the type file and the documentation.

[etimberg]

I looked at the code. It should support x/y assignment as well for padding

Chart.js/src/helpers/helpers.options.js

Lines 67 to 69 in c3a53f0

	export function toTRBL(value) {
	return _readValueToProps(value, {top: 'y', right: 'x', bottom: 'y', left: 'x'});
	}

so the documentation is correct. The correct change will be to update the typescript types to support X/Y assignment