encode development requirements in pyproject.toml (#32616)

Add a `project` block to the toml config along with development and CI
dependencies and a minimal `build-system` block, doing basically
nothing, so that spack can be bootstrapped to a full development
environment with:

```shell
$ hatch -e dev shell
```

or for a minimal environment without hatch:

```shell
$ python3 -m venv venv
$ source venv/bin/activate
$ python3 -m pip install --upgrade pip
$ python3 -m pip install -e '.[dev]'
```

This means we can re-use the requirements list throughout the workflow
yaml files and otherwise maintain this list in *one place* rather than
several disparate ones.  We may be stuck with a couple more temporarily
to continue supporting python2.7, but aside from that it's less places
to get out of sync and a couple new bootstrap options.

Co-authored-by: Adam J. Stewart <ajstewart426@gmail.com>

pyproject.toml

@@ -1,3 +1,74 @@
+[project]
+name="spack"
+description="The spack package manager"
+dependencies=[
+  "clingo",
+  "setuptools",
+  "six",
+  "types-six",
+]
+dynamic = ["version"]
+
+[project.scripts]
+spack = "lib.spack.spack_installable.main:main"
+
+[tool.hatch.version]
+path = "lib/spack/spack/__init__.py"
+
+[project.optional-dependencies]
+dev = [
+  "pip>=21.3",
+  "pytest",
+  "pytest-xdist",
+  "setuptools",
+  "click==8.0.2",
+  'black==21.12b0',
+  "mypy",
+  "isort",
+  "flake8",
+  "vermin",
+]
+ci = [
+  "pytest-cov",
+  "codecov[toml]",
+]
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[tool.hatch.build.targets.wheel]
+include = [
+  "/bin",
+  "/etc",
+  "/lib",
+  "/share",
+  "/var",
+  "CITATION.cff",
+  "COPYRIGHT",
+  "LICENSE-APACHE",
+  "LICENSE-MIT",
+  "NOTICE",
+  "README.md",
+  "SECURITY.md",
+]
+
+[tool.hatch.envs.default]
+features = [
+  "dev",
+]
+
+[tool.hatch.envs.default.scripts]
+spack = "./bin/spack"
+style = "./bin/spack style"
+test = "./bin/spack unit-test"
+
+[tool.hatch.envs.ci]
+features = [
+  "dev",
+  "ci",
+]
+
 [tool.black]
 line-length = 99
 target-version = ['py27', 'py35', 'py36', 'py37', 'py38', 'py39', 'py310']