consolidate source generation

[elringus]

This moves as much logic as possible out of source generator into the build step, which removes lots of duplicated code between the generator and the builder, as well as allows implementing common build preferences affecting bindings in all the assemblies.

Example on using new preferences attribute to make all bindings declared under "Foo.Bar" C# namespace have "Baz" namespace in JavaScript:

[assembly: JSPreferences(
    Space = ["^Foo\.Bar\.(\S+)", "Baz.$1"]
)]

Resolves #50, resolves #72.

Breaking changes:

• Removed [JSNamespace] attribute. Generated JS namespace is now customized via Space property of [JSPreferences] attribute.
• C# class name is now included in generated JS namespaces for both binding objects and types.
• Global is no longer prepended to the generated JS namespace when binding's type doesn't have namespace.
• Removed properties from [JSExport] and [JSImport] attributes, that allowed customizing some of the generated content. Associated behaviour (and more) is now customized via [JSPreferences] attribute.
• Main (entry) file name in generated JavaScript module changed to index.mjs.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (33e9742) 100.00% compared to head (0e15293) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #140   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           47        42    -5     
  Lines         1457      1425   -32     
  Branches       235       246   +11     
=========================================
- Hits          1457      1425   -32     

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