fix: SourceMapper correctly uses ModuleLoader to get source lines

[bartlomieju]

Fixes SourceMapper API that was changed in #823.

Now the source lines are correctly mapped even if deprecated SourceMapGetter API is not
used.

I need to add some tests too.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 74.46809% with 24 lines in your changes missing coverage. Please review.

Project coverage is 81.61%. Comparing base (0c7f83e) to head (490cc97).
Report is 63 commits behind head on main.

Files	Patch %	Lines
core/source_map.rs	72.41%	24 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #827      +/-   ##
==========================================
+ Coverage   81.43%   81.61%   +0.18%     
==========================================
  Files          97       98       +1     
  Lines       23877    24383     +506     
==========================================
+ Hits        19445    19901     +456     
- Misses       4432     4482      +50     

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