* ui: Allow text selection of clickable elements and their contents
This commit disables a click on mousedown be removing the `href`
attribute and moving it to a `data-href` attribute. On mouseup it will
only move it back if there is no selection. This means that an anchor
will only be followed on click _if_ there is no selection.
This fixes the fact that whenever you select some copy within a
clickable element it immediately throws you into the linked page when
you release your mouse.
Further notes:
We use the `isCollapsed` property here which 'seems' to be classed as
'experimental' in one place where I researched it:
https://developer.mozilla.org/en-US/docs/Web/API/Selection/isCollapsed
Although in others it makes no mention of this 'experimental' e.g:
- https://webplatform.github.io/docs/dom/Selection/isCollapsed/
- https://w3c.github.io/selection-api/#dom-selection-iscollapsed
I may have gone a little overboard in feature detection for this, but I
conscious of that fact that if `isCollapsed` doesn't exist at some point
in the future (something that seems unlikely). The code here will have
no effect on the UI. But I'd specifically like a second pair of eyes on
that.
* ui: Don't break right click, detects a secondary click on mousedown
* ui: Put anchor selection capability behind an ENV var
466c3c6899