#5866 Spacing in mid-staff clef changes

[Jean Abou Samra]

The spacing around mid-staff clef changes is unsufficient in some situations.

\version "2.21.0"

{
  r2.
  r4
  \clef bass
}

{
  r2.
  g'4
  \clef treble
}

{
  r2.. r32
  g'16.
  \clef treble
}

In the two first examples, the clef is too close to the
rest or note that precedes it. In the latter example, the
dot is closer to the clef than it is to the note.

[Jean Abou Samra]

Another instance that looks like a bug: spacing is completely confused when a clef change is immediately preceded by a grace note and followed by a full-bar rest.

\version "2.21.0"

{
  \grace { c''16 }
  \clef bass
  R1
}

What is happening here is that the full-bar rest always gets centered
in its measure regardless of other elements. This problem does not occur
usually since clefs are placed before the bar line. Grace notes are the only
case where a musical element and a full-bar rest take place in the same measure.