Allow Bracket Thickness to modify Square Brackets

Your idea

There's currently a small gap in features around brackets. MuseScore offers the most commonly-used bracket types (winged, curly, square, and floating), but Bracket thickness under Format>Style>System excludes square brackets. Either adding a new bracket to the palette, allowing the Style dialog to modify square brackets, or allowing brackets to stack/share columns would fill this small gap.

Problem to be solved

Older engraving conventions called for square brackets around choral staves, and these brackets were square with a bold line. It is currently impossible to natively create that effect in MuseScore.

Prior art

MuseScore can already draw a bold square bracket by stacking a square bracket and a line, but only when both elements are marked invisible (which disables their automatic placement):

Additional context

Examples of scores that uses this style of bracket:

Start by locating the Format > Style > System bracket-thickness setting and the square-bracket rendering or placement code. Compare the existing bracket types and the described invisible square-bracket-plus-line workaround. Done should mean that square brackets can produce the requested bold appearance natively, with the chosen behavior covered by appropriate validation.