Remove 'python setup.py' based build & test setup

Heavily refactor/rewrite the PKGBUILD to replace the setup.py dependent build and test process (TODO 0). To achieve this, the source has been heavily patched - the full patch set is maintained, and is easier to overview, in the 'archlinux' branch of my fork 1.

The first two patches, have already been upstreamed:

1. Ensure compatibility with Python 3.11 (#2212)
2. Remove imp module from tests to make them compatible with python 3.12 (#2251)

The following four I intend to try to upstream as they are generic fixes of various Python deprecations and removals:

3. Add missing import 'types'
4. Remove usage of 'imp' module - removed in Python 3.12
5. Remove usage of deprecated method locale.getdefaultlocale()
6. Fix invalid escape sequences

The following three workarounds to enable uilding and testing without setup.py:

7. Compile powerline executable without setuptools
8. Point shebangs to system Python
9. Remove failing tests

Additional changes to PKGBUILD:

• We now run a subset of the test suite, specifically the ones in tests/test_python with the exception of a few failing ones.

• The licenses is now installed as a one license file per package, to avoid the complexity of cross-package symlinks.

Resolves #1 (closed)