Support capturing code context from sourcesContent in the source map file

[waltjones]

Description of the change

Whether using source maps in Node.js or not, Rollbar.js has long had the ability to get code context (current line of code, plus surrounding lines) from the local source files at runtime.

This PR adds the ability to get this code context from the sourcesContent data in the source map file(s) when:

• The code is transpiled and has source maps. (For Node, this is usually Typescript.)
• The transpiled code and source maps are deployed away from the original sources.
• The source maps were generated with sourcesContent enabled.

Under the above conditions, code context will be captured successfully without access to the original source files.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Related issues

ch87007

#957

Development

• Lint rules pass locally
• The code changed/added as part of this pull request has been covered with tests
• All tests related to the changed code pass in development

Code review

• This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• "Ready for review" label attached to the PR and reviewers mentioned in a comment
• Changes have been reviewed by at least one other engineer
• Issue from task tracker has a link to this pull request

[bxsx]

Based only on the changes, it looks good to me.