Also fix some docstrings that were not valid rst.

Include build-system hook in via comments

Use meaningful names for fake build deps

Install static deps before requesting dynamic deps

Address review feedback

Remove python 3.7 from tox.ini

This should probably have been done in 51d9e1c (Drop support for
Python 3.7).

Use default labels for links

Add test coverage for Dependency

Introduce piptools.build module for building project metadata

Fix naming

Fixes for checkqa

Address feedback

Also
* remove unused `src_file` argument
* use filename as comes_from to avoid getting absolute paths in the
  output
* remove unused small-fake-c from fake_dists_with_build_deps
* mark tests as backtracking_resolver_only since the result is
  independent of resolver

Use Any type because mypy gives inconsistent results

Address feedback (II)

Assert exit code separately from stdout

Use intermediate variable

Move 'may be used more than once' to end of help text

Rename build-deps-only > only-build-deps

Use ALL_BUILD_DISTRIBUTIONS from already imported options

Use relative file path in comes from

Remove xfail

The test is failing locally since "Speed up tests execution (jazzband#1963)"
but the xfail should not be part of the PR.

Make pip-compile silent by default

Improve type hints in build

Remove excessive comments

Give build distribution literal a meaningful name

Test that transient build deps are excluded

Address feedback and adapt for build>1

Fix checkqa

Use build target terminology consistently

Use pathlib.Path consistently in build.py and new tests

More specific type hinting in build.py

Don't convert to absolute path unnecessarily

Update help texts

* Use "extract" instead of "install" in help texts
* Align texts that said different things but probably should be the same

Import Monkeypatch from public API

Under python versions >= 3.10 mypy will complain about

```
piptools/build.py:120: error: Unused "type: ignore" comment  [unused-ignore]
```

This causes pre-commit.ci to fail, presumably because it uses a recent
version of python.