Having some interactive elements forces the screen readers to switch to form mode
and consequently they delegate the keyboard stuff to the browser.
This patch sets an aria label on each editor in order to have a better description than just
'application'.
and tweak a bit the highlight one (e.g. it's useless to have 64 bits floating point numbers
when 32 bits ones are enough).
It's a required step for the refactoring of the ink tool (in order to use the draw layer).
It avoids to call several functions acting on the same SVG element.
One goal is to make the code for drawing with the Ink tool similar to the one to free highlighting:
it doesn't really make sense to have so different ways to do almost the same thing.
When the zoom level is high, it'll avoid to create a too big canvas covering all the page which consume
more memory, makes the drawing very slow and the overall user xp pretty bad.
A second goal is to be able to easily implement more drawing tools where we would just have to implement
how to draw from the pointer coordinates.
When playing with a pen, I noticed that sometimes a free highlight has still its
gray outline when an other one is drawn: for any reason the pointerleave event isn't
triggered.
There's a fair number of event listeners in the editor-code that we're currently removing "manually", by keeping references to their event handler functions.
This was necessary since we have a "global" `AbortController` that applies to all event listeners used in the editor-code, however it's now possible to combine multiple `AbortSignal`s; please see https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal/any_static
Since this functionality is [fairly new](https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal/any_static#browser_compatibility) the viewer will check that `AbortSignal.any()` is available before enabling the editing-functionality.
(It should hopefully be fairly straightforward, famous last words, for users to implement a polyfill to allow editing in older browsers.)
Finally, this patch also adds checks and test-only asserts to ensure that we don't add duplicate event listeners in various editor-code.
Given that we're removing event listeners with `AbortSignal` it's no longer necessary to keep a reference to a few of the event handler functions in order to remove them.
Hence we can simply inline the relevant `bind`-calls instead, which reduces the code-size a tiny bit.
Instead of sending to the main thread an array of Objects for a list of points (or quadpoints),
we'll send just a basic float buffer.
It should slightly improve performances (especially when cloning the data) and use slightly less memory.
The original bug was because the parent was null when trying to show
an highlight annotation which led to an exception.
That led me to think about having some null/non-null parent when removing
an editor: it's a mess especially if a destroyed parent is still attached
to an editor. Consequently, this patch always sets the parent to null when
deleting the editor.
The free highlighting is enabled when the mouse pointer isn't on some text.
Then we draw a shape with smoothed borders corresponding to the movement of
the mouse.
Printing/saving and changing the thickness will come later.
