Allow overriding the built-in glyph on widgets that hardcode one #436

Several widgets hardcode their symbol: Git Branch ⎇, Git Worktree 𖠰, Jj Bookmarks 🔖, Jj Workspace ◆, Git Conflicts ⚠, Git Ahead/Behind ↑/↓, Git Status !+*?, and the staged/unstaged/untracked markers. There is no way to change or suppress them; the only workaround is wrapping widgets in extra custom-symbol items, which clutters the line and still cannot replace the built-in glyph itself (#16 added custom-symbol widgets for adding icons, not replacing built-ins).

Ask: a per-widget way to set or clear the hardcoded glyph, covering multi-part widgets (Ahead/Behind, Git Status) where each part has its own symbol.