Unvendor pydoc_data and _pydecimal. ### Description

Removes / unvendors some python modules:

- Remove `_aix_support.py`, which is for supporting IBM AIX OS.

- Unvendor `_pydecimal.py`.
  - _pydecimal is a pure Python implementation of `decimal` module. [Importing `decimal` fallbacks](https://github.com/python/cpython/blob/main/Lib/decimal.py) to `_pydecimal` if the C-implementation `_decimal` is not available. In our case, _decimal is available, so _pydecimal will not be normally used. 

- Unvendor `pydoc_data`.
  - pydoc_data contains [a large (~700KB) dictionary](https://github.com/python/cpython/blob/main/Lib/pydoc_data/topics.py) for explaining python builtins. This is mostly used when `help("...")` is called.

### Checklists

- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
- [x] Add / update tests
- [x] Add new / update outdated documentation

package:
  name: boost-cpp
  version: 1.80.0
source:
  url: https://boostorg.jfrog.io/artifactory/main/release/1.80.0/source/boost_1_80_0.tar.gz
  sha256: 4b2136f98bdd1f5857f1c3dea9ac2018effe65286cf251534b6ae20cc45e1847
  patches:
    - patches/0001-config-libcpp15.patch

build:
  type: static_library
  script: |
    export INSTALL_DIR=${WASM_LIBRARY_DIR}
    ./bootstrap.sh --prefix=${INSTALL_DIR}

    ./b2 variant=release toolset=emscripten link=static threading=single \
      --with-date_time --with-filesystem \
      --with-system --with-regex --with-chrono --with-random --with-program_options --disable-icu \
      cxxflags="$SIDE_MODULE_CXXFLAGS -fexceptions -DBOOST_SP_DISABLE_THREADS=1" \
      cflags="$SIDE_MODULE_CFLAGS -fexceptions -DBOOST_SP_DISABLE_THREADS=1" \
      linkflags="-fpic $SIDE_MODULE_LDFLAGS" \
      --layout=system -j"${PYODIDE_JOBS:-3}" --prefix=${INSTALL_DIR} \
      install

about:
  home: https://www.boost.org/
  summary: Free peer-reviewed portable C++ source libraries.

package:
  name: boost-cpp
  version: 1.80.0
source:
  url: https://boostorg.jfrog.io/artifactory/main/release/1.80.0/source/boost_1_80_0.tar.gz
  sha256: 4b2136f98bdd1f5857f1c3dea9ac2018effe65286cf251534b6ae20cc45e1847
  patches:
    - patches/0001-config-libcpp15.patch

build:
  type: static_library
  script: |
    export INSTALL_DIR=${WASM_LIBRARY_DIR}
    ./bootstrap.sh --prefix=${INSTALL_DIR}

    ./b2 variant=release toolset=emscripten link=static threading=single \
      --with-date_time --with-filesystem \
      --with-system --with-regex --with-chrono --with-random --with-program_options --disable-icu \
      cxxflags="$SIDE_MODULE_CXXFLAGS -fexceptions -DBOOST_SP_DISABLE_THREADS=1" \
      cflags="$SIDE_MODULE_CFLAGS -fexceptions -DBOOST_SP_DISABLE_THREADS=1" \
      linkflags="-fpic $SIDE_MODULE_LDFLAGS" \
      --layout=system -j"${PYODIDE_JOBS:-3}" --prefix=${INSTALL_DIR} \
      install

about:
  home: https://www.boost.org/
  summary: Free peer-reviewed portable C++ source libraries.
