Refactor: split the build() into smaller pieces

[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.

• Split the build() function into smaller pieces: prepare(), metadata() and build().
• Call prepare_metadata* hook to get the metadata, instead of building the whole wheel.
• Switch to importlib.metadata to parse the metadata.

[codecov-commenter]

Codecov Report

Merging #543 (33e8c43) into main (085d2b7) will decrease coverage by 0.02%.
The diff coverage is 79.55%.

@@            Coverage Diff             @@
##             main     #543      +/-   ##
==========================================
- Coverage   82.94%   82.91%   -0.03%     
==========================================
  Files          68       68              
  Lines        5500     5497       -3     
  Branches      982      968      -14     
==========================================
- Hits         4562     4558       -4     
- Misses        656      662       +6     
+ Partials      282      277       -5     

Flag	Coverage Δ
unittests	82.77% <78.22%> (-0.09%)	⬇️

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

Impacted Files	Coverage Δ
pdm/resolver/providers.py	95.40% <50.00%> (ø)
pdm/utils.py	71.11% <66.66%> (-0.37%)	⬇️
pdm/models/candidates.py	75.22% <71.22%> (-7.55%)	⬇️
pdm/models/requirements.py	93.93% <90.47%> (-0.79%)	⬇️
pdm/builders/__init__.py	100.00% <100.00%> (ø)
pdm/builders/base.py	91.72% <100.00%> (+0.05%)	⬆️
pdm/builders/editable.py	86.66% <100.00%> (ø)
pdm/builders/sdist.py	100.00% <100.00%> (ø)
pdm/builders/wheel.py	100.00% <100.00%> (ø)
pdm/cli/actions.py	75.64% <100.00%> (ø)
... and 7 more

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