doc: expand history for conditional exports changes in v12
As discussed on #42336 this change adds some extra detail to the history of unflagging conditional exports across v12.16 and v2.17. In v13 conditional exports became fully unflagged in v13.7 when --experimental-conditional-exports
was removed.
Unfortunately the version order linting rule doesn't allow putting the removal of --experimental-modules
for just 12.17.0 above the removal of --experimental-conditional-exports
in both 12.16.0 and 13.7.0, but hopefully the change there is still clear.
Fixes: #36162