Migrates from the deprecated toCommandLineShell to toCommandLineShellGNU.
This changes the output format to use GNU-style concatenated options
(--line-height=28) and adds shell escaping for values with special
characters (e.g., '#1e1e2e' becomes '--ab=#1e1e2e'). The format
was verified to work correctly with bemenu.
Signed-off-by: Austin Horstman <khaneliman12@gmail.com>