Copied license files may be overwritten

[L-TChen]

Describe the bug
Multiple license files are allowed in a cabal package description, but their relative paths are not preserved when installing.
Therefore, if the same file name is used in different directories, then only the last entry will be kept.

To Reproduce
Steps to reproduce the behavior:

1. Consider any .cabal file with an entry:

  license-files: LICENSE somedir/LICENSE

2. Then, install this project

$ cabal install ...

3. In the directory ~/.cabal/store/ghc-x.y.z/<mingled_pkgname>/share/doc/, there will be only one LICENSE which is a copy of the last LICENSE.

Expected behavior
Their relative path should be kept.

In particular, takeFileName should be removed from L185 in

cabal/Cabal/src/Distribution/Simple/Install.hs

Lines 179 to 185 in f465da4

	let lfiles = licenseFiles pkg_descr
	unless (null lfiles) $ do
	createDirectoryIfMissingVerbose verbosity True docPref
	for_ lfiles $ \lfile' -> do
	let lfile :: FilePath
	lfile = getSymbolicPath lfile'
	installOrdinaryFile verbosity lfile (docPref </> takeFileName lfile)

Additional context
I intend to fix this in #9172 as well.