Make Cabal agnostic about working directory

This commit makes the library functions in Cabal agnostic of the working
directory. In practice, this means that we distinguish `FilePath`s
from un-interpreted `SymbolicPath`s. The latter may be paths that are
relative to the working directory, and need to be interpreted with
respect to a passed-in argument specifying the working directory,
instead of using the working directory of the current process.
See Note [Symbolic paths] in Distribution.Utils.Path.

In particular, paths in the package description now use the SymbolicPath
abstraction, which allows specifying whether they are allowed to be
absolute, and, if they are relative, what they are relative to.
For example, source files are relative to a source search directory,
data files are relative to the data directory, and doc files are
relative to the package root.

Fixes #9702

CI changelogs: switch to XDG, fix cache key

This is the same as #9845 but for the changelogs.yml workflow.

`changelog-d` currently has restrictive bound `base < 4.19` which we
need to ignore if we want to build on the latest GHC as shipped by the
GHA runner.

Fix #9815: fix caching for quick-jobs CI (XDG, cache keys)

Not sure why this was not up to date on master and still CI passed.
Maybe the content of this file is dependent on the GHC version we are
using to build the `get-cabal-macros` tool?

The `lexer` target was removed in
https://github.com/haskell/cabal/pull/8980

Fix #9815:
- Cache `~/.local/state/cabal` instead of `~/.cabal/store`
- `~/.local/bin` is used instead of `~/.cabal/bin` and is already in the PATH
  (verify this by calling `alex` after installing it)

As I am passing by:
- bump cache action to v4
- double-quote `$USER` to keep actionlint happy
- move `if` from shell-level to job-level
- allow newest `alex`

CI validate-old-ghcs: pin to haskell-actions/setup@v2.6

This provides temporary life support to the `validate-old-ghcs` action
until node16 will be finally axed by GHA in May 2024.

Workaround for:
- https://github.com/haskell/cabal/issues/9858

Add “Add default-language” suggestion

As a warning (“Hackage would reject this package”), to prepare users
to GHC language editions.

Ignore testdb/intree generated files

Use package groups

* Remove cabal.project.libonly

It was only referenced once in a stale Makefile comment about doctests.

* Remove weeder

- remove weeder's configuration
- remove its recipe from Makefile
- remove its project

* Delete cabal.project.doctest

- Adding --ghc-options="-Wwarn" is sufficient to avoid the numerous <interactive> failures seen otherwise
- write-ghc-environment-files has a default of never

- Reduce duplication in test flag setup
- Avoid "New config" picking cabal's own project

Before this change, this was the test failure:

Unit Tests
  UnitTests.Distribution.Client.Configure
    Configure tests
      New config:                     FAIL
        Exception: project-cabal/pkgs/cabal.config: withBinaryFile: does not exist (No such file or directory)
        Use -p '/New config/' to rerun this test only.
      Replacement + new config:       OK
      Old + new config:               OK
      Old + new config, no appending: OK
      Old + new config, backup check: OK
      Local program options:          OK

1 out of 6 tests failed (0.02s)

- Satisfy -Wmissing-signatures in test-runtime-deps
- Satisfy -Wx-partial in HackageBenchmark
- Satisfy -Wunused-imports in QuickCheck.Instances.Cabal
- Use partial pattern for filtering in list comprehension
- Don't error on deprecated import

- Move constraints to project-cabal/constraints.config
- Remove duplicate package groups
- Groups coverage, doctest and validate are the same as the default group
- Remove duplicate validate-libonly package group
- Both validate and validate-libonly are the same
- Move Cabal & Cabal-syntax to pkgs/cabal.config
- Add install package group
- Add benchmarks package group
- Add tests package group
- Both default and libonly groups were the same set of packages that I renamed to tests
- Put install group before tests and benchmarks
- Don't repeat packages
- Add TODO and REVIEW comments on allow-newer exceptions
- Move latest.ghc configuration
- Put program-options first & separate imports
- Remove optional-packages
- Don't reiterate default value for tests and benchmarks
- Don't reiterate default value for optimization
- Add ghc-options.config
- Rename to ghc-latest.config
- Use -Werror in ghc-options.config
- Don't include ghc-options.config for doctest project
- Add project-config/pkgs.config
- Add project-config/pkgs.config importing all package groups
- Move Cabal-described to the cabal package group
- Remove cabal.project.buildinfo
- Have cabal.project.doctest import cabal.project
- Split integration tests into their own package group.
- Add back trailing newlines at EOF in projects
- Integration-tests.config needed for libonly
- Add a README for projects.

Fix --project-file option for boostrap

Text file, newlines at end of files

Add required-fields to changelog.d config

Conform BSD-2-Clause and BSD-3-Clause text to SPDX

`cabal init` text for BSD-2-Clause and BSD-3-Clause licence differed
slightly from the one published at SPDX. [1] [2]

This caused some problems to users when dealing with licence-recognition
software. [3]

[1] https://spdx.org/licenses/BSD-2-Clause.html
[2] https://spdx.org/licenses/BSD-3-Clause.html
[3] https://discourse.haskell.org/t/non-standard-license-generated-by-stack-new/9059

Add a --dry-run build check of cabal.project.release

Co-authored-by: brandon s allbery kf8nh <allbery.b@gmail.com>