feat: support pypa build (#521)

* feat: support pypa build

fix: update `cibuildwheel.linux.troubleshoot` to know about build

Workaround issue with PyPy venv module by installing build[virtualenv]

fix: test_dependency_constraints_file when using build

fix: test/test_pep518.py

fix: use `strtobool` to parse `CIBW_PYPA_BUILD`

fix: update `cibuildwheel.linux.troubleshoot` to know about `python -m pip wheel`

test: use `build_mode` in `test/test_dependency_versions.py` tests

* refactor: use build-backend instead

* Apply suggestions from code review

Co-authored-by: Joe Rickerby <joerick@mac.com>

* refactor: use literal types for build_frontend

* refactor(tests): build_mode -> build_frontend_env

* Update test/test_before_build.py

Co-authored-by: Joe Rickerby <joerick@mac.com>

test/conftest.py

@@ -1,7 +1,9 @@
+from typing import Dict
+
 import pytest
 
 
-def pytest_addoption(parser):
+def pytest_addoption(parser) -> None:
     parser.addoption(
         "--run-emulation", action="store_true", default=False, help="run emulation tests"
     )
@@ -11,7 +13,7 @@ def pytest_configure(config):
     config.addinivalue_line("markers", "emulation: mark test requiring qemu binfmt_misc to run")
 
 
-def pytest_collection_modifyitems(config, items):
+def pytest_collection_modifyitems(config, items) -> None:
     if config.getoption("--run-emulation"):
         # --run-emulation given in cli: do not skip emulation tests
         return
@@ -19,3 +21,10 @@ def pytest_collection_modifyitems(config, items):
     for item in items:
         if "emulation" in item.keywords:
             item.add_marker(skip_emulation)
+
+
+@pytest.fixture(
+    params=[{"CIBW_BUILD_FRONTEND": "pip"}, {"CIBW_BUILD_FRONTEND": "build"}], ids=["pip", "build"]
+)
+def build_frontend_env(request) -> Dict[str, str]:
+    return request.param  # type: ignore