Issue 5168 Let arpeggio-bracket/slur depend on grob-property thickness

Before, used thickness based only on line-thickness from layout.
For brackets it's now the multiplication of line-thickness and grob's
thickness.
Slur-style-arpeggios now rely on grob-properties thickness and
line-thickness, both multiplies with layout line-thickness.
Similiar to real Slurs.