Issue 5084: Create Bracket class

Issue 5084: Create Bracket class

Code involving brackets suffers from two confusing
organizational issues:

(1) Tuplet_bracket::make_bracket is used to create brackets
for a number of grobs: BassFigureBracket, HorizontalBracket,
OttavaBracket, PianoPedalBracket, VoltaBracket, along with
TupletBracket

(2) Methods belonging to Horizontal_bracket are used to draw
both horizonal brackets (HorizontalBracket) and vertical
brackets (BassFigureBracket)

To remedy this, a new Bracket class is created.

This new class contains the old Tuplet_bracket::make_bracket,
Horizontal_bracket::make_bracket, and
Horizontal_bracket::make_enclosing_bracket.

These methods have been renamed to clarify their purpose.