Move and reimplement convert_number_to_words.py

[tianyizheng02]

Describe your change:

• Move convert_number_to_words.py from web_programming/ to conversions/ (fixes web_programming/convert_number_to_words.py is not web programming #8881)
• Reimplement the algorithm from scratch because the logic was very opaque and too heavily nested—I didn't consider the current implementation to be salvageable
• Add support for the Western numbering system (both short and long) because the original implementation only supported the Indian numbering system (lakh and crore but no million, billion, etc)
• Add extensive doctests and error handling to handle edge cases and disallow too-large inputs

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".