PR #78793 moved the code that this test was testing for into `NDEBUG`
blocks, which means that only exist in assert toolchains. The test was
not changed, so it was failing in non-assert toolchains.
Replace the process_fine_grained_swiftdeps.sh with a python equivalent
(which also preserves the horrendous handling of YAML and even
"faithfully" replicates the horrible global variables). This enables a
number of tests on Windows although the instigating macro test is not
yet enabled due to the need for further tweaks to the tests.
