[luatex] Bad skips with display math

[Javier Bezos]

Hello,

Consider the following document, typeset with 1.13.2 (TeX Live 2021/W32TeX):

==================================

Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
$$(a+b)^2 = a^2+2ab+b^2 \eqno (1.10)$$
Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
$$(a+b)^2 = a^2+2ab+b^2 \leqno (1.10)$$
Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

\textdir TRT \pardir TRT \bodydir TRT \pagedir TRT

Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
$$(a+b)^2 = a^2+2ab+b^2 \eqno (1.10)$$
Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
$$(a+b)^2 = a^2+2ab+b^2 \leqno (1.10)$$
Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

\bye

===================================

The result is http://www.texnia.com/archive/luamathskip.pdf

As you can see, the labels are reversed, but the calculations for
the vertical skips, based on the previous line, are not. Either
the labels shouldn’t be reversed (which makes sense for me,
because conceptually we are in math and not in a paragraph) or
the calculations have to be fixed.

Please, fix also the long standing bug which misplaces the label
with leqno when \pardir (but no other dirs) is set to TRT.

Javier