Since commit cc21d0e478 (Utilities/Sphinx: Make signatures linkable,
2023-03-09) we always convert `cmake:command` domain cross-references to
use the explicit `text <text>` form. This breaks the XRefRole's
`fix_parens` setting that we use to render `cmd` as `cmd()`.
Instead, transform `cmd(sub)` to `cmd(sub) <cmd(sub)>` to preserve
the sub-command link destination, but leave `cmd` alone and let
XRefRole convert it to `cmd()`.
c8679f0571