r300: expose PIPE_CAP_LEGACY_MATH_RULES

r300: expose PIPE_CAP_LEGACY_MATH_RULES

We are already doing the 0*anything = 0 by default and we are also
using the DX versions of math ops like RCP. It looks like R300 and
R400 can't do IEEE math anyway (but its hard to tell without docs).
For R500 we can do IEEE math, but testing showed that some apps
are dependent on the DX behavior, so considering we only advertise
GLSL 1.20 where this is left ot the driver, just keep the curent
status and expose PIPE_CAP_LEGACY_MATH_RULES so that nine can stop
emiting math workarounds.

Also fixes two Xnine tests.

Signed-off-by: Pavel Ondračka <pavel.ondracka@gmail.com>
Reviewed-by: Filip Gawin <filip@gawin.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17007>