Obey USE_MY_METRICS in compound glyphs

Obey USE_MY_METRICS in compound glyphs

* src/sfnt.c (struct sfnt_compound_glyph_context): New fields
holding the positions of both phantom points.
(sfnt_decompose_compound_glyph): New argument METRICS_RETURN;
return the metrics of components with USE_MY_METRICS within this
field.
(sfnt_decompose_glyph): New argument METRICS_RETURN, which
serves the same purpose.
(sfnt_build_glyph_outline): Apply glyph advance and origin
distortion to METRICS, and return the metrics as altered by
compound glyphs in there.
(sfnt_lookup_glyph_metrics): Trim away two unused parameters,
PIXEL_SIZE and HEAD, whose functionality has been superseeded by
sfnt_scale_metrics and the implicit scaling the interpreter
performs.
(sfnt_interpret_compound_glyph_2): Save phantom points within
fields provided to that end in CONTEXT.
(sfnt_interpret_compound_glyph_1): Save and source phantom
points for each glyph to and from the context.
(sfnt_test_get_metrics, main): Adjust tests correspondingly.

* src/sfnt.h: Update prototypes.

* src/sfntfont.c (sfntfont_get_metrics): Remove obsolete
parameters.
(sfntfont_get_glyph_outline): Don't change temp by the metrics
distortions, which is now the task of sfnt_decompose_glyph.

(cherry picked from commit ea3d211f3f7ecc5b59d5affc1aed812a2ded62b0)