Python

Build python as a dependency of vim when the `--build-dependencies`
option is set.

Change log:
* replace skip-dependencies with build-dependencies (not set by default)
* script for building python (vim dependency)
* build python and use over system version for vim installation if  is set
* add CI job to build vim with built version of python
4 jobs for 4-python in 24 minutes and 25 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
passed tmux #8017
docker

00:05:42

passed vim #8015
docker

00:05:28

passed vim_build_dependencies #8016
docker

00:08:39

passed zsh #8014
docker

00:04:34