BUG: Preserve index order when constructing DataFrame from dict
- [x] closes #24859
- [x] tests added / passed
    (no new tests added)
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

This resolves the issue of `pd.DataFrame(dict)` or `pd.DataFrame.from_dict(dict)` not preserving the order of the index specified in `dict`.

This required fixing up tests that relied on alphabetical ordering. The changes to these tests also test for this new preserved ordering; let me know if I should add an additional explicit test.