Refactoring in preparation of #11411

This commit includes a series of refactorings that are necessary to
solve #11411:

- Abstract the Rebuild monad into the MonadRebuild typeclass,
  introducing the `withRunRebuildInIO` method of MonadRebuild. This
  allows us to interleave plain `IO` with `MonadRebuild` without
  necessarily having to use `Rebuild` itself. This is especially
  important because `Rebuild` also encodes the "current working
  directory" concern, which is relevant within `cabal-install`, but
  something we don't want to require within the `Cabal` library. Since
  the `MonadRebuild` typeclass allows for arbitrary custom monadic state
  per instance, it can live in the `Cabal` subproject, together with
  operations defined in terms of the typeclass, while `Rebuild` itself
  remains in `cabal-install`, using the custom monadic state to cover
  the "current working directory" concern.
- Change the `StateT` part of `Rebuild` into `WriterT`, since we only
  ever emit additional files from within a Rebuild context; consuming
  them happens on the outside, so Writer is sufficient.
- Provide `MonadRebuild` instances for the existing `Rebuild` type, and
  for the most minimal type that can satisfy the typeclass, `WriterT
  [MonitorFilePath] IO`.
- Implement most file monitoring / Rebuild actions in terms of
  `MonadRebuild`, so they can live in `Cabal`
  (`Distribution.Simple.RebuildMonad`), leaving only
  `cabal-install` specific things in the existing `cabal-install`
  module (`Distribution.Client.RebuildMonad`). Specifically, we
  implement `rerunIfChanged'` in terms of `MonadRebuild` and a custom
  function for chaining `IO` actions (serially or in parallel, as
  needed); the existing `rerunIfChanged` and
  `rerunConcurrentlyIfChanged` functions, which live in `cabal-install`,
  are now implemented in terms of `rerunIfChanged'`, which lives in
  `Cabal`).
- Move large parts of the `Distribution.Client.FileMonitor` module from
  `cabal-install` to `Cabal` (as `Distribution.Simple.FileMonitor`);
  we will be needing these parts to solve #11411
  (`Distribution.Client.FileMonitor` still re-exports all of them
  though).
- Move most of the `Distribution.Client.HashValue` module over to
  `Cabal` (with the exception of TUF-related functions, which are
  specific to `cabal-install`; again we re-export everything in
  `cabal-install` to maintain API compatibility).
- Move `getFilePathRootDirectory` from `Distribution.Client.Glob` into
  `Distribution.Simple.FileMonitor.Types` - it has little to do with
  actual globs, and is only used for file monitoring purposes.
- Shuffle some utility functions around to make them accessible where we
  need them.

The big picture with all this is that we want to reuse the existing file
monitoring machinery to keep track of build-tool versions alongside
generated source files. However, the tracking needs to happen in the
`Cabal` library, while file monitoring has so far only been available in
`cabal-install`; hence we need to move the required file monitoring code
and its dependencies into the `Cabal` library, but without introducing
any `cabal-install` specific concerns into `Cabal`, and without breaking
API compatibility on the `cabal-install` side.

Provide minimal `MonadRebuild` instance

Author: tdammers

Cabal/Cabal.cabal

@@ -42,8 +42,11 @@ library
     , Cabal-syntax ^>= 3.17
     , array      >= 0.4.0.1  && < 0.6
     , base       >= 4.13     && < 5
+    , base16-bytestring >= 1.0 && < 1.1
+    , binary     >= 0.7.3    && < 0.9
     , bytestring >= 0.10.8   && < 0.13
     , containers >= 0.5.8.2  && < 0.9
+    , cryptohash-sha256 >= 0.11 && < 0.12
     , deepseq    >= 1.3.0.1  && < 1.7
     , directory  >= 1.2.7    && < 1.4
     , filepath   >= 1.4.2    && < 1.6
@@ -121,11 +124,13 @@ library
     Distribution.Simple.Compiler
     Distribution.Simple.Configure
     Distribution.Simple.Errors
+    Distribution.Simple.FileMonitor
     Distribution.Simple.FileMonitor.Types
     Distribution.Simple.Flag
     Distribution.Simple.GHC
     Distribution.Simple.GHCJS
     Distribution.Simple.Haddock
+    Distribution.Simple.HashValue
     Distribution.Simple.Glob
     Distribution.Simple.Glob.Internal
     Distribution.Simple.Hpc
@@ -153,6 +158,7 @@ library
     Distribution.Simple.Program.Script
     Distribution.Simple.Program.Strip
     Distribution.Simple.Program.Types
+    Distribution.Simple.RebuildMonad
     Distribution.Simple.Register
     Distribution.Simple.Setup
     Distribution.Simple.ShowBuildInfo