[css-round-display] device-radius media query replacement

We (Shane, Florian, Tab, me, Simon Pieters) had a side-discussion at the
face-to-face meeting (during break) about what we want instead of
https://drafts.csswg.org/css-round-display/#device-radius-media-feature .

Tab initially wanted to just have three keyword categories
(essentially rectangular, rounded-corners, circular/ellitical), but
I'm very hesitant to have more than two categories, because I think
we either want media queries to be boolean or to be numeric.

Florian wanted a query to reflect (I think) whether a box with
length or percentage corner-radius (for circular or elliptical
corners) fits entirely within the display; or something like that; I
can't accurately reflect the details.  Tab wasn't happy about this
messing with numeric-sorting aspects of media queries, although I
pointed out that some of these objections are less serious in MQ4
with its better not, they're still a serious pitfall for authors.  I
proposed a slight variant that messed with media queries less, in
which there were separate queries for the most-rounded rectangle
that contained the screen, and the least-rounded rectangle that fits
entirely inside the screen, but that option didn't seem particularly
clearer.

But Shane pointed out that in real cases, treating the corners
separately is important, and furthermore proposed that what we
really want is not tests for rounding, but tests for whether placing
something at a particular point on the display will be visible in
the screen.

This led to the conclusion that what we really want is a media query
for whether certain points (probably specifiable in different
coordinate systems, e.g., polar, percentages, pixels) are visible
within the display.  We had a bit of discussion about whether points
are sufficient, or whether we really want the test to be for squares
or rectangles being inside the display.  (We considered circles, but
I thought that testing a square or rectangle is generally more
useful because things like text tend to be rectangles.)

I think at this point the next step would be somebody writing up a
proposal for how to fit this (relatively complex) query inside of
media queries.

(This is intended to fit into the minutes to explain some of what
happened during the break, since there was discussion both before
and after the break.)

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                          https://www.mozilla.org/   𝄂
             Before I built a wall I'd ask to know
             What I was walling in or walling out,
             And to whom I was like to give offense.
               - Robert Frost, Mending Wall (1914)