feat: Depcrate SourceMapGetter, move methods to ModuleLoader

[bartlomieju]

This commit deprecates SourceMapGetter trait, JsRuntime::source_map_getter
option and updates ModuleLoader trait to have the same methods as
SourceMapGetter.

In real usage it's always implementor of ModuleLoader that also implements
SourceMapGetter. It makes little sense to keep these two trait separate.

This will open up doors for native source map support that is being
developed in #819.

SourceMapGetter is scheduled to be removed in 0.297.0.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 57.14286% with 15 lines in your changes missing coverage. Please review.

Project coverage is 81.53%. Comparing base (0c7f83e) to head (562768e).
Report is 60 commits behind head on main.

Files	Patch %	Lines
core/source_map.rs	50.00%	8 Missing ⚠️
core/modules/loaders.rs	30.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #823      +/-   ##
==========================================
+ Coverage   81.43%   81.53%   +0.09%     
==========================================
  Files          97       98       +1     
  Lines       23877    24324     +447     
==========================================
+ Hits        19445    19833     +388     
- Misses       4432     4491      +59     

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[littledivy]

LGTM