Expose SourceMapView.get_source_contents function

[pablomatiasgomez]

Currently only a few functions of the underlying lib (https://github.com/getsentry/rust-sourcemap) are exposed.

In particular, there's currently no way to get the source code contents, but just the names can currently be retrieved.

This change adds support to expose the fn SourceMap::get_source_contents : https://github.com/getsentry/rust-sourcemap/blob/24a07e376a634c7823ada1b55326454ba7fc921d/src/types.rs#L787-L792

[pablomatiasgomez]

I just organized the functions here as they were sorted differently in each of the files.

[loewenheim]

Hi, thank you for the contribution! Can you add an entry to the top of the changelog? Something like

## Unreleased

**Features**

- python bindings: Expose SourceMapView.get_source_contents function. ([#921](https://github.com/getsentry/symbolic/pull/921))

[pablomatiasgomez]

Hi, thank you for the contribution! Can you add an entry to the top of the changelog? Something like

## Unreleased

**Features**

- python bindings: Expose SourceMapView.get_source_contents function. ([#921](https://github.com/getsentry/symbolic/pull/921))

sure! Added! Thanks for the review :)