feat: remove usages of __file__ to support pdm in a zipapp

[frostming]

Pull Request Check List

• A news fragment is added in news/ describing what is new.
• Test cases added for changed code.

Describe what you have changed in this PR.

Use importlib.resources to read script or data inside the package, to replace the usages of __file__ variable. This will enable PDM to be used in a zipapp.

TODO

• Update unearth to support being used in ziapp
• Provide a way to get the PDM version in zipapp

[codecov-commenter]

Codecov Report

Base: 85.36% // Head: 85.37% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (e707d92) compared to base (7f09f24).
Patch coverage: 85.41% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1567      +/-   ##
==========================================
+ Coverage   85.36%   85.37%   +0.01%     
==========================================
  Files          91       91              
  Lines        8068     8081      +13     
  Branches     1911     1920       +9     
==========================================
+ Hits         6887     6899      +12     
- Misses        793      794       +1     
  Partials      388      388              

Flag	Coverage Δ
unittests	85.19% <85.41%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/pdm/core.py	88.52% <0.00%> (ø)
src/pdm/cli/actions.py	78.07% <20.00%> (-0.44%)	⬇️
src/pdm/__version__.py	71.42% <50.00%> (-1.30%)	⬇️
src/pdm/utils.py	86.91% <66.66%> (ø)
src/pdm/cli/commands/run.py	91.59% <100.00%> (-0.04%)	⬇️
src/pdm/cli/commands/self_cmd.py	71.52% <100.00%> (ø)
src/pdm/cli/utils.py	83.23% <100.00%> (+0.43%)	⬆️
src/pdm/models/in_process/__init__.py	100.00% <100.00%> (ø)
src/pdm/models/specifiers.py	79.29% <100.00%> (+0.14%)	⬆️

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