refactor(changelog): support --bump for processed releases

[orhun]

Description

This is a behavior change to improve the --bump functionality.

--bump flag now takes the processed commits into account which means e.g. if you have used commit_preprocessors to modify the commit message, the bumped version will be calculated based on these modified commit messages.

There is also another behavioral change in the --bumped-version. For multiple repositories, it used to return the each calculated version separated by newline. However, this functionality is not documented anywhere and I'm not sure if it is really useful. This feature is not released yet which means it was safe to remove. I might consider adding it again if there will be desire in the future.

Motivation and Context

See #405

How Has This Been Tested?

Unit tests.

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (no code change)
• Refactor (refactoring production code)
• Other

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.
• I have formatted the code with rustfmt.
• I checked the lints with clippy.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-commenter]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (f635bae) 44.39% compared to head (40dcf53) 45.72%.

Files	Patch %	Lines
git-cliff/src/lib.rs	0.00%	11 Missing ⚠️
git-cliff-core/src/changelog.rs	75.00%	3 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #408      +/-   ##
==========================================
+ Coverage   44.39%   45.72%   +1.33%     
==========================================
  Files          13       13              
  Lines         712      711       -1     
==========================================
+ Hits          316      325       +9     
+ Misses        396      386      -10     

Flag	Coverage Δ
unit-tests	45.72% <39.14%> (+1.33%)	⬆️

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