Respect glyph metrics modified by instruction code

* src/sfnt.c (sfnt_read_glyph): Clear advance and origin
distortion returning an empty glyph.
(sfnt_build_instructed_outline): New parameter *ADVANCE_WIDTH,
in which the glyph's advance width is saved.
(sfnt_interpret_compound_glyph_1): Refine commentary.
(sfnt_verbose, main): Adjust tests.

* src/sfnt.h: Update prototypes correspondingly.

* src/sfntfont.c (sfntfont_get_glyph_outline): If an instructed
outline is available, derive the advance and lbearing from the
measurements within.
(sfntfont_probe_widths): Call sfntfont_measure_pcm to establish
average widths.
(sfntfont_open): Do so after instruction code initialization
completes.
(sfntfont_measure_pcm): Revise commentary.
2 jobs for master in 46 minutes and 8 seconds (queued for 8 seconds)
Status Job ID Name Coverage
  Build Images
failed #78800
build-image-inotify

00:46:08

 
  Normal
skipped #78801
test-src-inotify
 
Name Stage Failure
failed
build-image-inotify Build Images
5f70bf18a086: Retrying in 1 second
dbdb1f162c4e: 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-9aea075f: No such file or directory
ERROR: Job failed: exit code 1