* Improve their accessibility by giving both links a full label
("Jump to x" and "Jump to y" instead of "Jump to: ", "x", "y").
This also makes things better for localisation.
* Use pure CSS for the toggling of the visibility on focus,
instead of relying on JavaScript. Especially given the
JS came from core's 'jquery.mw-jump' module, which is
considered technical debt per T195256.
* Use plain <a> links in the HTML instead of wrapped in a <div>.
This solves the long-standing problem whereby the margin
between #contentSub and #mw-content-text had to be awkwardly
negated and overridden.
Bug: T195256
Change-Id: I40a769ee3a822a5a9167ec1d144e6b151eb8e141
6dccc0d96e