Doc: bump to Python 3.10; Sphinx 5.3.0. Remove `--constraint: foo -none` & some polishing

For the moment, readthedocs.org does not support Sphinx 6.

- `PACKAGE -none` as already been removed in 3.4 as valid constraint.
(I guess this is now flag syntax.)

- Important constraint `installed` was just buried in an example, I made
it stand out more in a bullet point.
Same for `source`, even though this is an exotic constraint.

- Highlight constraint `installed` in connection with `allow-newer`.

- Group `test` and `bench` constraint with the `+/-FLAG` constraints.

Fixup: Apply concrete suggestions from code review

Fixes suggested by @ulysses4ever, thanks@

Co-authored-by: Artem Pelenitsyn <a.pelenitsyn@gmail.com>

* Apply command line flags to install packages (#8637)

* remove expectBroken on NonIgnoredConfigs test

---------

Co-authored-by: gbaz <gershomb@gmail.com>

CI: add GHC pre-release

Had to block lib/cli-suite tests on Windows, see discussion starting here:

- https://github.com/haskell/cabal/pull/8754#issuecomment-1435025848

- -XTypeInType is deprecated
- skip failing JS test on Windows
  Cf. https://github.com/haskell/cabal/pull/8754#issuecomment-1435535763
- deal with lift2A in Prelude since base-4.18 (GHC 9.6)
- disable everfailing Backpack tests

* Disallow GHC <8.0

closes #8715

* Add changelog entry

cabal-testsuite: new `instance Show TestEnv`

The `Show` instance for `TestEnv` is helpful in debugging testcases.
While it produces large Haskell expressions not for consumption by the
naked eye, it can be inspected in viewers like `ppshow`.

https://hackage.haskell.org/package/pretty-show

The field `testRecordNormalizer :: String -> String` of the `TestEnv`
record seems to be a hook to arbitrarily reformat the recorded output
of a test.  However, it is ever only set to `id`.

On the other hand, being of function type, this field prevents us from
deriving a `Show` instance.  Thus, it is being removed as dead code.

Fix `config` format docs.

Documentation says “config (same format as cabal.project)”, but
it is an internal binary format.

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

don't auto-download in hash validation phase

* (cabal init) make BSD-3-Clause default

* Add changelog for #8757

* Modify test to incorporate new BDS-3 default

---------

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Bump cabal-bootstrap-gen to GHC 9.4.4 ecosystem

I updated the dependencies in the .cabal bootstrap file and
sightly adjusted src/Main.hs for the `I.riCabal → I.riCabalHash`
change.

Fixes #8613

doctests: switch to the preffered method of calling the tool

which is `cabal repl --with-ghc=doctest`. This not only catches up with
the current upstream recommendations, but also simplifies the usage:
before this change calling doctest required you to set up an environment
with QuickCheck available (we used to do it via cabal-env). The new
method takes care of it automatically.

Also add some docs to fix #8147

Revert "Fix project-local build flags being ignored."

This reverts commit b547ead5
from https://github.com/haskell/cabal/pull/8623.
Unexpected side-effect has been found, so these code
improvements have to be done differently.
The other commit in the PR is a test and it's retained.

Changing a file from `extra-source-files` causes `cabal build` to
reevaluate the build plan, judging from the following behavior.

```console
$ cabal build
...

$ cabal build
Up to date

  # Make a change to any of the extra-source-files, e.g. Foo.txt

$ cabal build
...
In order, the following would be built (use -v for more details):
 - ... (lib) (file Foo.txt changed)
...
```

One notes here that the 3rd `cabal build` does not just output "Up to date".

cabal run +RTS warning