JDK-8233218 revealed we don't have automatic test coverage for icon configuration of Linux packages produced by jpackage.

Sanity testing of icon configuration should be added to jdk.jpackage.test.FileAssociations test helper.

We should verify the value of `--size` parameter of `xdg-icon-resource` command in install/uninstall scripts of deb/rpm packages contain not a random integer, but one of recognized icon sizes (See https://linux.die.net/man/1/xdg-icon-resource for the list of common con sizes).