Fix the icon button directionality in right-to-left languages.
Previously, the button was hardcoded to support left-to-right only.
- Replace the skin.vector.icons' `.mw-ui-icon-wikimedia-{name}:before`
`selector` in skin.json with a placeholder, `{name}`. I don't think
this selector should be needed but it seems to be erroneous not have
one. I believe this issue of wanting a null selector was encountered
in Minerva or MobileFrontend but am unable to locate the past
discourse.
- Add check and unchecked menu button selectors to skin.json that set
the appropriate background image. This shards some of the styles out
of Less and into ResourceLoader-land but it's worthwhile.
- Revise the name of horizontal collapse icon to describe its form not
function, "collapseHorizontal" to "chevronHorizontal". This has been
an established convention that was missed a couple patches back.
- Add a flipped chevronHorizontal for RTL. I used Inkscape to do the
flip and tried to match the style of the original by hand. Feel free
to edit further.
- Drop the now unnecessary icon flipping JavaScript and initial Mustache
class. This enables a real CSS-only solution for the icons.
Bug: T246419
Change-Id: I60f65b3c595bf18d309b667d9a0b066691b90c97
