* scm/output-lib.scm (grace-spacing::calc-shortest-duration): new function.

* scm/output-lib.scm (grace-spacing::calc-shortest-duration): new function.

* scm/define-grob-properties.scm (all-user-grob-properties):
remove grace-space-factor.

* scm/define-grob-interfaces.scm (grace-spacing-interface): add grace-spacing-interface
(spacing-options-interface): add.

* ly/engraver-init.ly (AncientRemoveEmptyStaffContext): add Grace_spacing_engraver

* lily/spacing-options.cc (get_duration_space): move function from spacing-basic.cc

* lily/spacing-basic.cc (note_spacing): do init_from_grob on
GraceSpacing object.

* lily/note-spacing.cc: fix prop list formatting

* lily/beaming-pattern.cc (de_grace): new function. Sensible
beaming for grace notes too.

* input/regression/spacing-grace.ly: update.

* lily/grace-spacing-engraver.cc: new file.

* lily/spacing-spanner.cc: add strict-grace-spacing.