bpo-45629: Add a test for the "freeze" tool. (gh-29222)

The "freeze" tool has been part of the repo for a long time. However, it hasn't had any tests in the test suite to guard against regressions. We add such a test here. This is especially important as there has been a lot of change recently related to frozen modules, with more to come.

Note that as part of the test we build Python out-of-tree and install it in a temp dir.

https://bugs.python.org/issue45629