Reject unconstrained dependency = none|all|eq

[philderbeast]

Fixes #11468. Adds an eq option for --reject-unconstrained-dependencies. Extends the solving failure reason message to include =all or =eq.

Manual QA

With this repository, cabal freeze.

Edit cabal.project.freeze commenting out the line for the pretty dependency.

-             any.pretty ==1.1.3.6,
+          -- any.pretty ==1.1.3.6,

Now cabal build cabal-install-solver --reject-unconstrained-dependencies=? will only build when ? is none.

Edit cabal.project.freeze changing the line for the pretty dependency.

-             any.pretty ==1.1.3.6,
+             any.pretty >0,

Now cabal build --reject-unconstrained-dependencies=? will build when ? is none|all but won't build when ? is eq.

$ cabal build cabal-install-solver --reject-unconstrained-dependencies=eq
Warning: this is a debug build of cabal-install with assertions enabled.
Resolving dependencies...
Error: [Cabal-7107]
Could not resolve dependencies:
[__0] trying: Cabal-3.17.0.0 (user goal)
[__1] next goal: pretty (dependency of Cabal)
[__1] fail (not a user-provided goal nor mentioned as a constraint,
  but reject-unconstrained-dependencies=eq was set)
[__1] fail (backjumping, conflict set: Cabal, pretty)
After searching the rest of the dependency tree exhaustively,
  these were the goals I've had most trouble fulfilling: Cabal, pretty

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