Fix #7126: Stricter checks for relative paths

E.g. `foo/../../../bar` is now forbidden. That cannot work.

WIP: Add SymbolicPath, use for hs-source-dirs

Tell the time per file in hackage-tests parsec

Move tests from Cabal to Cabal-tests package

ReadP is not Parsing

The are various motivation points:
- I'm not aware anyone third party running Cabal tests (maybe nixpkgs?)
- No need to do gen-extra-source-files, as Cabal-tests is not distributed
- No multiple rebuilds of Cabal-QuickCheck, Cabal-tree-diff
- Slightly smaller Cabal sdist (which is quite big still)

release.py builds from sdist tarballs

Add --concurrently to solver-benchmarks

Make solver-benchmark use fresh cabal-dirs

Add nothunks test for parser

This way they won't remake caches on each run,
allowing to compare vastly different cabals.

Prohibit empty file paths.

Because there are plenty of `license-file: ""` and `data-dir: ""`,
out there, parser accepts and
filters out or transforms to "." respectively.

There are just two files which have non-empty filepath somewhere
else, namely in `hs-source-dirs:`. These are handler by `Quirks`.

Warning increase:

```diff
-40411 files contained warnings
+41163 files contained warnings
```

Rewrite cabal syntax file

Pr 6972 extra packages

The discussion in #6952 indicated that extra-packages stanzas wouldn't
quite work yet. It turns out in order for cabal to find exes for
already installed extra-packages we need to also consider `installed`
packages when pruning the install plan.

Includes some changes to OutputNormalizer

Resolve #7090: Remove v2-build beta note from --help

Nix style local builds have become the default

Resolve #7091: Require custom-setup for cabal-version: 1.24 and later

Add SPDX License list 3.10

Fix command notes being replaced by descriptions

This was causing the description of "new" prefixed and unprefixed
commands to be printed at both the top and bottom of their help text.

PR #6295: hsc2hs options

Motivation: I (simonmar) want to use hsc2hs with C++, which requires

```
hsc2hs-options: --cc=g++ --lflag=-lstdc++
```

We pass `hsc2hs-options` before or after `--cc` and `-lflag`,
depending on the version of `hsc2hs`.

I (phadej) added a tests:
- hsc2hs-options are passed to `hsc2hs` (but not to GHC e.g.).
- `--cc` has expected effect

`g++` tests doesn't seem to work on Windows, due mingw ncurses linkage
issue, https://github.com/msys2/MINGW-packages/issues/3531
We also need non-ancient hsc2hs (>= 0.68).