gh-36885: Switch more Python toolchain packages to use (platform-independent) wheels
<!-- ^^^^^
Please provide a concise, informative and self-explanatory title.
Don't put issue numbers in there, do this in the PR body below.
For example, instead of "Fixes #1234" use "Introduce new method to
calculate 1+1"
-->
<!-- Describe your changes here in detail -->
We simplify the Sage distribution by installing more Python packages as
platform-independent wheels.
- No longer use direct installation using the deprecated `setup.py
install`
- `pip` bootstraps itself from its wheel
- `setuptools` is installed as a wheel
- remove the 2nd copy of setuptools (SPKG `setuptools_wheel`)
We also add the build backends `hatchling` and `flit_core` to
`PYTHON_TOOLCHAIN`. This fixes some missing dependencies, including
`editables` (as reported in https://groups.google.com/g/sage-
release/c/uP-rwlM__MU/m/oU-49z9VAwAJ).
The package `deprecation` is no longer used by any package (has it been
... deprecated?) and is removed here.
<!-- Why is this change required? What problem does it solve? -->
<!-- If this PR resolves an open issue, please link to it here. For
example "Fixes #12345". -->
<!-- If your change requires a documentation PR, please link it
appropriately. -->
### :memo: Checklist
<!-- Put an `x` in all the boxes that apply. -->
<!-- If your change requires a documentation PR, please link it
appropriately -->
<!-- If you're unsure about any of these, don't hesitate to ask. We're
here to help! -->
<!-- Feel free to remove irrelevant items. -->
- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.
### :hourglass: Dependencies
<!-- List all open PRs that this PR logically depends on
- #12345: short description why this is a dependency
- #34567: ...
-->
- Depends on #36888 (for fixing the html workflow)
<!-- If you're unsure about any of these, don't hesitate to ask. We're
here to help! -->
URL: https://github.com/sagemath/sage/pull/36885
Reported by: Matthias Köppe
Reviewer(s): Dima Pasechnik
