Follow-up of bpo-36142, add _Py_PreInitialize() function to "pre-initialize" Python:

* initialize memory allocators
* initialize LC_CTYPE locale and UTF-8 Mode

Py_Initialize() should also be modified to no longer coerce the C locale or enable the UTF-8 Mode:
https://bugs.python.org/issue36202#msg337915

See also:

* bpo-36202: Calling Py_DecodeLocale() before _PyPreConfig_Write() can produce mojibake
* bpo-36204: Deprecate calling Py_Main() after Py_Initialize()? Add Py_InitializeFromArgv()?

New changeset 74f6568bbd3e70806ea3219e8bacb386ad802ccf by Victor Stinner in branch 'master':
bpo-36301: Add _PyWstrList structure (GH-12343)
https://github.com/python/cpython/commit/74f6568bbd3e70806ea3219e8bacb386ad802ccf

New changeset 625997622b4736e9184bdd8bf1e22a7b51be1afc by Victor Stinner in branch 'master':
bpo-36301: _PyCoreConfig_Read() ensures that argv is not empty (GH-12347)
https://github.com/python/cpython/commit/625997622b4736e9184bdd8bf1e22a7b51be1afc

New changeset c183444f7e2640b054956474d71aae6e8d31a543 by Victor Stinner in branch 'master':
bpo-36301: Fix Py_Main() memory leaks (GH-12420)
https://github.com/python/cpython/commit/c183444f7e2640b054956474d71aae6e8d31a543

New changeset 5f9cf23502febe0eb3bc02e45c7d2bfc79424757 by Victor Stinner in branch 'master':
bpo-36301: Error if decoding pybuilddir.txt fails (GH-12422)
https://github.com/python/cpython/commit/5f9cf23502febe0eb3bc02e45c7d2bfc79424757

New changeset f29084d611a6ca504c99a0967371374febf0ccc3 by Victor Stinner in branch 'master':
bpo-36301: Add _PyRuntime.pre_initialized (GH-12457)
https://github.com/python/cpython/commit/f29084d611a6ca504c99a0967371374febf0ccc3

New changeset fa1537684869186da7938e4330361bf02363bac8 by Victor Stinner in branch 'master':
bpo-36301: Add _PyPreCmdline internal API (GH-12458)
https://github.com/python/cpython/commit/fa1537684869186da7938e4330361bf02363bac8

In term of API, we get something like:

    _PyInitError err;

    _PyPreConfig preconfig = _PyPreConfig_INIT;
    preconfig.utf8_mode = 1;
    preconfig.allocator = "malloc";

    _PyInitError err = _Py_PreInitializeFromPreConfig(&preconfig);
    if (_Py_INIT_FAILED(err)) {
        _Py_ExitInitError(err);
    }

    /* PyMem_RawMalloc and Py_DecodeLocale can now be used */

    _PyCoreConfig config = _PyCoreConfig_INIT;
    config.user_site_directory = 0;

    err = _Py_InitializeFromConfig(&config);
    if (_Py_INIT_FAILED(err)) {
        _Py_ExitInitError(err);
    }

    /* ... use Python ... */

    Py_Finalize();

    /* Note: no need to "free" preconfig nor config memory, they use constants */

New changeset 6d5ee973f0600a3a9444f569dcf0dd346bfa2a11 by Victor Stinner in branch 'master':
bpo-36301: Add _PyRuntimeState.preconfig (GH-12506)
https://github.com/python/cpython/commit/6d5ee973f0600a3a9444f569dcf0dd346bfa2a11

New changeset f72346c47537657a287a862305f65eb5d7594fbf by Victor Stinner in branch 'master':
bpo-36301: Cleanup preconfig code (GH-12535)
https://github.com/python/cpython/commit/f72346c47537657a287a862305f65eb5d7594fbf

Note for myself: is there a problem between the priority of PYTHONHOME env var and pybuilddir.txt configuration file?

New changeset a6fbc4e25e1dc7d1c9a26888b9115bc6c2afc101 by Victor Stinner in branch 'master':
bpo-36301: Add _Py_PreInitializeFromConfig() (GH-12536)
https://github.com/python/cpython/commit/a6fbc4e25e1dc7d1c9a26888b9115bc6c2afc101

New changeset 1075d1684ab84dc7c28d93cfb46e95e70d3b6d3b by Victor Stinner in branch 'master':
bpo-36301: Add _Py_GetConfigsAsDict() function (GH-12540)
https://github.com/python/cpython/commit/1075d1684ab84dc7c28d93cfb46e95e70d3b6d3b

New changeset f78a5e9ce8f32a195f5f788aade79578437f30a6 by Victor Stinner in branch 'master':
bpo-36301: Add _Py_GetEnv() function (GH-12542)
https://github.com/python/cpython/commit/f78a5e9ce8f32a195f5f788aade79578437f30a6

New changeset 20004959d23d07ac784eef51ecb161012180faa8 by Victor Stinner in branch 'master':
bpo-36301: Remove _PyCoreConfig.preconfig (GH-12546)
https://github.com/python/cpython/commit/20004959d23d07ac784eef51ecb161012180faa8

Note for myself: PYTHONDEVMODE=1, PreConfig isolated=1, CoreConfig isolated=0: is the dev mode enabled or not? IMHO it should not. Maybe add a specific unit test?

New changeset f8ba6f5afc317d1be3025db1be410ac66a7e5a27 by Victor Stinner in branch 'master':
bpo-36301: Cleanup preconfig.c and coreconfig.c (GH-12563)
https://github.com/python/cpython/commit/f8ba6f5afc317d1be3025db1be410ac66a7e5a27

I created a follow-up issue: bpo-36443.

--

> Note for myself: PYTHONDEVMODE=1, PreConfig isolated=1, CoreConfig isolated=0: is the dev mode enabled or not? IMHO it should not. Maybe add a specific unit test?

PR 12569 adds these tests.

The feature has been implemented, I close the issue. The work is continued in other issues.

New changeset 6a8c3139ae9ada89d4a95985ec7cf8bb7d03bc01 by Victor Stinner in branch 'master':
bpo-36301: Fix _PyPreConfig_Read() compiler warning (GH-12695)
https://github.com/python/cpython/commit/6a8c3139ae9ada89d4a95985ec7cf8bb7d03bc01