Unify component `pad` logic

[etpinard]

PR #989 added pad to update menus, and PR #986 with to do same for sliders.

At the moment, colorbars are using xpad and ypad to determine their horizontal padding ➡️ we should switch them to pad.l + pad.r (++ add a backward-compatible cleanLayout step) and add support for pad.t and pad.b while at it.

We should also allow legends, range selector and range sliders to set their own pad options.

[etpinard]

cc @rreusser

[rreusser]

Copying checklist from #985.

• sliders
• updatemenus
• legend
• range selector
• colorbar
• rangeslider
• review code for others?

[rreusser]

For reference, the procedure is pretty simple:

1. When computing its size, a component should, as a final step, add padding in each direction.
2. It sends this size to automargins
3. it must shift the content it draws (presumably by pad.l and pad.t)

[jensb]

Would this enable users to configure legend entry padding as well? (Not just the whole legend)
IMHO, the legend entries have too much padding around them especially when using smaller fonts. I would like to be able to configure this.

[etpinard]

@jensb you mean like in #881 ?

[jensb]

No, I meant the vertical padding. When using smaller font sizes, the padding between legend rows is (IMHO) too large. I think it's hardcoded as 5 pixels in both directions (?). I would like to be able customize this padding, e.g. using a configuration variable. There is 'tracegroupgap' but I would like to have 'tracegap' - also possibly smaller(!) than the default.

[jensb]

Can somebody please have a look at this and maybe give me a hint how to make legend entry padding configurable? I'm not afraid of hacking by myself and creating a pull request, but I need some startup assistance. Thank you!

[gvwilson]

Hi - this issue has been sitting for a while, so as part of our effort to tidy up our public repositories I'm going to close it. If it's still a concern, we'd be grateful if you could open a new issue (with a short reproducible example if appropriate) so that we can add it to our stack. Cheers - @gvwilson