Verify briefcase.integrations.__all__ is accurate

[rmartin16]

After I merged the ToolCache typing changes in to my Windows codesigning PR, I expected the new tests to fail. When they didn't fail, adding this additional check seemed prudent....since we're already this far in.

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[rmartin16]

Actually....do not merge this.

The call to inspect.getmembers() operates on briefcase.integrations.__dict__.....which is influenced by the setting of briefcase.integrations.__all__.

I'll need to investigate further....something like pkgutil.iter_modules looks promising.

[rmartin16]

Ok. pkgutil reports all modules in a package.

>>> pprint(list(m.name for m in pkgutil.iter_modules([os.path.dirname(briefcase.integrations.__file__)])))
['android_sdk',
 'base',
 'cookiecutter',
 'docker',
 'download',
 'flatpak',
 'git',
 'java',
 'linuxdeploy',
 'rcedit',
 'subprocess',
 'windows_sdk',
 'wix',
 'xcode']

Unlike inspect.getmembers():

>>> for module, _ in inspect.getmembers(sys.modules[f"briefcase.integrations"], inspect.ismodule):
...     if module not in nontool_modules:
...         print(f"{module=}")
...
module='android_sdk'
module='cookiecutter'
module='docker'
module='download'
module='flatpak'
module='git'
module='java'
module='linuxdeploy'
module='rcedit'
module='subprocess'
module='visualstudio'
module='wix'
module='xcode'

[freakboy3742]

👍 A good safety check to add - thanks!