Accessibility: erratic keyboard navigation in Effects dialog

Greetings,
so far the Effects dialog in VLC 4 is the same as in 3 (AFAICS),
which means now would probably be a good time to tackle keyboard
navigation in that dialog.

Open the Effects dialog with Ctrl-E; click in it to get the focus
(see #25757). Now go directly to the Video Effects tab (you can
use Ctrl-Tab but it will depend on where the focus is: for example
if you’re on the Save/Close buttons it won’t do anything).
Now, in the Essentials sub-tab, hitting Tab once brings you to the
“Image adjust” checkbox; checking it (with Space) opens up a bunch of
relevant parameters which you can Tab through.
Surprise: if you hit Space whilst you’re in these parameters (unless
you’re on “Brightness Threshold”, which is itself a checkbox rather
than a slider) will actually disable the whole “Image adjust” panel,
rendering all the sliders you were browsing through instantly moot.
No problem then: hitting Space again should re-check the “Image adjust”
box and open them up again, right? Wrong: the focus has actually now
moved onto the next checkbox, “Sharpen”.
Similarly, hitting Space a few times on that box checks and unchecks
it; but if you happen to be on the slider below it, hitting Space
will not only uncheck it but bring you to the next checkbox, and so on.

Let’s move on to the next sub-tab, “Crop”. Visually, you can see four
spin buttons, with values for Top, Left, Right and Bottom variables.
Here’s where hitting Tab a few times will bring you though, in
sequential order:

• “Top” value.
• “Bottom” value.
• “Synchronize top and bottom”.
• “Synchronize left and right”.
• and only then, “Left”…
• … and “Right”.

If you’ve enabled “Synchronize top and bottom”, the “Bottom” value has
now become moot (but you have no way to know that other than visually);
if you’ve enabled “Synchronize left and right”, there’s no more “Right”
value to be set.

Onto the “Colors” sub-tab -- my favorite. Here’s where Tab brings you:

• “Color threshold” (tough it’s visually below “Color extraction”)
• “Color extraction”. Fun thing: if you check that box, then you’ll need
  to Shift-Tab to access the relevant text box setting, rather than using
  Tab.
• “Negate colors”, then “Posterize”, then “Gradient”. So far so good.
• If you check “Gradient”, then hitting Tab brings you NOT onto the
  dropdown menu that’s just below it visually, but onto the next couple
  of checkboxes, “Color” and “Cartoon”. Then that dropdown should at least
  come next, right? Wrong: you’ll need to Tab through the whole window and
  find it eventually, weirdly stuck in-between the “Color extraction” text
  box and the “Color extraction” checkbox. Why???

In the next “Geometry” sub-tab, likewise, the items are out of order and
the “Rotate” area is lost below (or on top of) everything else for some reason.

Ditto for “Add text” in the “Overlay” sub-tab; the “Advanced” sub-tab is a
mess when comparing the visual layout with the keyboard navigation but at
least when taking only one of these into account it’s actually usable.

The reason why I’m getting fired up over this is that Video Effects are
actually a powerful and crucial Accessibility asset for impaired users;
to them, proper keyboard navigation (and, em, actual vocalization, see
#25166) is not just a nice feature to have: it’s a deal-breaker.