cabal-install: Fix non-reinstallable package set (backport #9092) (#9141)

cabal-install: Fix non-reinstallable package set

In #9064 we discovered that `ghc-boot` was added to the
non-reinstallable package set due to #8051 despite there being no
reason why it can't be built from its source distribution. This
revealed the fact that there is quite some ambiguity around what
constitutes a non-reinstallable package.

In #9064 we worked out a hopefully-more-clear picture of
non-reinstallability. Here we update the commentary to describe this
concept and update the lists to reflect the new definition.

Closes #9064.

(cherry picked from commit 2e32a44f)

# Conflicts:
#	cabal-install/src/Distribution/Client/Dependency.hs

* Fix tests

(cherry picked from commit 249374d1)

# Conflicts:
#	cabal-install/tests/UnitTests/Distribution/Solver/Modular/Solver.hs

* Fix conflicts