Issue 3649: Fill in section "\set vs \override"
Doc-fr: Issue 3649: Fill in section "\set vs \override"
Let #{ 4 #} be a duration while #{ 4 \cm #} stays a length

An UNSIGNED not followed by a NUMERIC_IDENTIFIER inside of #{ ... #}
is interpreted as a duration rather than a number.  Also, inside
of #{ ... #} no "numeric expressions" using binary operators +-*/ are
interpreted.

The behavior of (signed and unsigned) integers and numeric expressions
in assignments and as function arguments rather than inside
of #{ ... #} is not affected.
Use #{ 4 #} and #{ c #} for duration/pitch in optional-args regtest
Interpret #{ -3 #} as postevent rather than negative number

Since #{ 4 #} is interpreted as duration rather than number, interpreting
negative integers as numbers rather than fingering is not really helpful.
Issue 3648/1: Isolated durations in music sequences now stand for unpitched notes

This allows for things like

\new RhythmicStaff { 4 4. 8 4 | 4 \tuplet 3/2 { 2 4 } 4 }

"unpitched" simply means that this is rendered as a normal NoteEvent,
but the pitch information is missing and has to be filled in by some
other means.  The example using RhythmicStaff is not actually
commendable as the MIDI rendition still requires a pitch or drum
type.  It's just that as of this patch, there are no immediately
useful applications.  The rhythmic shorthand { c4 4. 8 4 } is
introduced by a later patch.
Issue 3648/2: Slight documentation amendment for RhythmicStaff in NR
Let copy-repeat-chord return the copy target for efficiency
Issue 3648/3: Pitchless durations inherit previous pitch when scorifying

This turns { c4 4 4 4 } into { c4 c4 c4 c4 } and
\drummode { tamb4 4 4 4 } into \drummode { tamb4 tamb4 tamb4 tamb4 }.
Issue 3648/4: Let \displayLilyMusic deal with pure rhythms
Issue 3648/5: Explain isolated durations in NR "Rhythms"
Issue 3648/6: Regtest for rhythmic sequences.
Issue 3648/7: Give several examples of durations without explicit pitches
Run scripts/auxiliar/makelsr.py
Merge branch 'issue3648' into staging

Contains enough related commits that its better to do as one merge
commit for the sake of bisection and/or reverting.
Fold function_arglist_backup_common into function_arglist_backup

After the last refactoring, function_arglist_backup does not need a closed
variant, so there is no point in an extra non-terminal.
parser: move FRACTION into embedded_scm_bare_arg

It's a closed expression; not having to parse it with separate rules
reduces the amount of cruft in the rules.
Make make_music_from_simple return music rather than a list in \chordmode
Let a PITCH_IDENTIFIER optionally be followed by octave modifiers

This makes pitch identifiers more similar to note names.  There is no
point in keeping the distinction just for triggering syntax errors
on music that has no sensible other interpretation.
Make sure optional arguments accepted as pitches stay pitches when reparsing