refactor: turn Python generator into a service

[lars-reimann]

Summary of Changes

Turn the Python generator into a service. The CLI now calls this service instead of containing the entire implementation.

This has several advantages:

• It facilitates testing, since no files have to be created on disk anymore.
• It also makes it easier to integrate the Python generator into VS Code, since it no longer has to go through the CLI.
• It reduces dependencies between CLI, language, and VS Code, which might help when restructuring the repo using NPM workspaces.

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ JSON	eslint-plugin-jsonc	2	0	0	2.36s
✅ JSON	jsonlint	2		0	0.24s
✅ JSON	npm-package-json-lint	yes		no	0.73s
✅ JSON	prettier	2	0	0	1.41s
✅ JSON	v8r	2		0	4.72s
✅ REPOSITORY	git_diff	yes		no	0.05s
✅ TYPESCRIPT	eslint	6	0	0	8.22s
✅ TYPESCRIPT	prettier	6	0	0	2.0s

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[codecov]

Codecov Report

Merging #692 (ef77107) into main (60112bf) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #692   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           72        71    -1     
  Lines         9534      9475   -59     
  Branches      1908      1907    -1     
=========================================
- Hits          9534      9475   -59     

Files	Coverage Δ
...rc/language/generation/safe-ds-python-generator.ts	100.00% <100.00%> (ø)
src/language/safe-ds-module.ts	100.00% <100.00%> (ø)
src/language/validation/names.ts	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes