Add password show/hide symlinks for Plasma 6

[swomf]

Plasma 6 relies on icons named password-show-off and password-show-on for the password visibility button. This commit adds symlinks for each that point to hint.svg and visibility.svg respectively.

Fixes #3671.

Demonstration (kscreenlocker)

Before:

password hidden

password shown

After:

password hidden

password shown

[SmartFinn]

Thanks. The symlinks have to use relative path to targets instead of absolute. Could you fix it? Please run the following commands inside the cloned repo on your machine:

cd tools/work/
./new-symlink.sh actions hint.svg password-show-off.svg
./new-symlink.sh actions view-hidden.svg password-show-on.svg
./convert.sh
./put-into-theme.sh
git add -u
git commit -m "Fix password-show-on and password-show-off symlinks"
git push

I can't change this PR because you didn't create a separated branch for it.