This makes a series of changes to SplitButtonView designed to solve

visual inconsistencies with other buttons, improve placement and

animation, preventing a problem where the button appeared below the

draft banner, and preventing the button appearing out of nowhere after

the review draft banner loads.
The button now makes use of the new segmented button CSS rules in order

to create a single outer button that then has segments for the label and

drop-down arrow. These rules ensure that the button looks consistent

with other buttons in the draft banner and Review Dialog. The segmented

button takes care of the outer border appearance, letting us simplify

the CSS a bit for the split button. The CSS has been simplified further

by way of having classes set on the split button's element instead of

the various child elements.
The button's menu is no longer placed on the document body. Instead,

it's placed within the container of the split button, alongside the

segmented button. This avoids having to figure out a z-index, which

wasn't working anymore on the draft banner (as that calculation

depended on the banner being in the DOM, which it hasn't been for a

while). It also doesn't set left anymore. This lets the menu align

automatically with the button.
The button and menu's width is no longer managed the same way. The

button itself never changes width anymore, using the natural width

instead (preventing it from appearing very long if the menu is long).

The menu is now set to be at least as long as the button (using widths

with subpixel-precision, instead of rounded client widths), and is set

to not wrap (forcing it to extend beyond the button's width if needed,

instead of wrapping, which is presumably why the buttons' width

originally needed to be set).
Animation is now controlled via CSS transitions instead of using

jQuery's fading functions. This does require a timeout with a value

matching the one used in CSS, but it otherwise enables much smoother

animations.
There are also fixes for presentation when there's multiple entries in

the menu.
And finally, the publish button on the draft banner no longer simply

pops into existence after loading the page. The HTML for the button is

now pre-populated on the banner. It will be replaced on load, but this

prevents a weird transition after page load.

Tested the Publish Review button on macOS (Chrome, Firefox, Safari) and

Windows (Chrome, Firefox, IE, Edge) in both the draft banner and the

Review Dialog.
Loaded the page and saw that the Publish Review button was there

immediately, and did not have any visual jump when the draft banner fully

loaded.
Injected additional items temporarily into the Publish Review buttons and

verified that the entries all had correct styles in both pop-down and pop-up

modes.
Replaced the current item with one containing a short label. Verified that

the menu had the button's exact width in both pop-down and pop-up modes.