Bring GX point interpolation further into standards compliance

* src/sfnt.c (sfnt_infer_deltas_2): New function; factor much of
sfnt_infer_deltas_1 into this function, then modify its
treatment of untouched points positioned at their reference
points to align with standard GX treatment.
(sfnt_infer_deltas_1): Remove all code not concerning anchor
point discovery.
(main): Adjust tests.
2 jobs for master in 52 minutes and 3 seconds (queued for 10 seconds)
Status Job ID Name Coverage
  Build Images
failed #79194
build-image-inotify

00:52:03

 
  Normal
skipped #79195
test-src-inotify
 
Name Stage Failure
failed
build-image-inotify Build Images
5f70bf18a086: Retrying in 2 seconds
5f70bf18a086: Retrying in 1 second
net/http: request canceled (Client.Timeout exceeded while awaiting headers)
Running after script...
$ test -n "$(docker ps -aq -f name=${test_name})" && docker cp ${test_name}:checkout/test ${test_name}
$ test -n "$(docker ps -aq -f name=${test_name})" && docker rm ${test_name}
$ find ${test_name} ! \( -name "*.log" -o -name ${EMACS_TEST_JUNIT_REPORT} \) -type f -delete
find: build-image-inotify-f80f1b23: No such file or directory
ERROR: Job failed: exit code 1