Add support for symlinked license dir
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symlink rule: remove the trailing slash when checking the existence of symlink target as it can be inconsistent.
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licensepkg rule: detect if the license dir is a symlink, and check the existence of the license files in the linked package if it's a dependency.
This eliminates the following false positive errors (qt5-* packages usually have a symlinked license dir to qt5-base):
qt5-multimedia E: Missing custom license directory (usr/share/licenses/qt5-multimedia)
qt5-multimedia E: Symlink (usr/share/licenses/qt5-multimedia) points to non-existing /usr/share/licenses/qt5-base