Added vowel transitions for lyrics

ly/property-init.ly

 % property-init.ly
 
 \version "2.21.0"
 
 %% for dashed slurs, phrasing slurs, and ties
 #(define (make-simple-dash-definition dash-fraction dash-period)
     (list (list 0 1 dash-fraction dash-period)))
 
 %% common definition for all note head styles reverting
 %% (palm mute, harmonics, dead notes, ...)
@@ skipping 737 matching lines @@
 }
 
 
 %% volta brackets
 
 allowVoltaHook =
 #(define-void-function (bar) (string?)
   (_i "Allow the volta bracket hook being drawn over bar line @var{bar}.")
                        (allow-volta-hook bar))
 
+
+%% vowel transitions
+
+vowelTransition = #(make-music 'VowelTransitionEvent)
+
+
 %% x notes
 
 #(define (cross-style grob)
 ;; Returns the symbol 'cross to set the 'style-property for (Tab-)NoteHead.
 ;; If the current text-font doesn't contain the glyph set 'font-name to '()
 ;; and 'font-family to 'feta.
 ;; If 'feta is replaced by another music-font without cross-style-glyphs
 ;; note-head.cc throws a warning and no visual output happens.
   (let* ((layout (ly:grob-layout grob))
          (props (ly:grob-alist-chain grob))
@@ skipping 19 matching lines @@
    (if (eq? (ly:music-property note 'name) 'NoteEvent)
        #{ \tweak style #cross-style $note #}
        #{ \xNotesOn $note \xNotesOff #}))
 
 %% dead notes (these need to come after "x notes")
 
 % Define aliases of cross-head notes for specific purposes
 deadNotesOn  = \xNotesOn
 deadNotesOff = \xNotesOff
 deadNote     = #xNote