Enable tabbing to Run button

[hturner]

comment from @ajrgodfrey

The run button should come after the script window so that a screen reader can tab from the script window directly to the run button. Currently, tab does not exit the script window: you can arrow out but not tab out and tab is the more usual way to navigate.

[ajrgodfrey]

Two issues. Order is currently run before editing space. Moving that to after is more intuitive. Second issue relates to getting out of the script editing. Once a screen reader is taken out of editing mode, we should be able to tab (or back-tab) but this didn't work for me, leaving me having to arrow down (or up)

[georgestagg]

In 7df7964 I tweaked the order of HTML elements so that the Editor component comes just before the Run button when using Tab navigation.

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There is a tricky issue here in that the Editor component has been configured so that it captures Tab and Shift-Tab for functionality relating to the indenting of code.

However, there is an escape hatch. If you press the Escape key first, and then the Tab key immediately after, the focus will be moved to the next element, as normal. Similarly for Escape and then Shift-Tab.

I have added a paragraph element to the page, hidden from sighted users, that explains this unexpected functionality. The element has then been linked to the Editor component through its aria-describedby attribute.

As with the other changes, the webR website will take a little while to update, but the changes should be available by tomorrow.