Continuing work towards #8988.
The first five commits were created using stubdefaulter on various Python versions; the following commits were all created manually by me to fix various problems. The main things this adds that weren't present in #9501 are:
- Defaults in Windows-only modules and Windows-only branches (because I'm running a Windows machine)
- Defaults in non-py311 branches
- Defaults for float parameters
- Defaults for overloads
* Move code from `decimal.pyi` to `_decimal.pyi`
The stub previously did `from decimal import *` in `_decimal.pyi`, but the opposite happens at runtime.
