Add source and source properties to StyleManagerProtocol

[julianrex]

Continuation of #317

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Fixes: < Link to related issues that will be fixed by this pull request, if they exist >

Pull request checklist:

• Briefly describe the changes in this PR.
• Write tests for all new functionality. If tests were not written, please explain why.
• Add example if relevant.
• Document any changes to public APIs.
• Apply changelog label ('breaking change', 'bug 🪲', 'build', 'docs', 'feature 🍏', 'performance ⚡', 'testing 💯') or use the label 'skip changelog'
• Add an entry inside this element for inclusion in the mapbox-maps-ios changelog: <changelog>Refactored Style source and source property management.</changelog>.
• Update the migration guide, API Docs, Markdown files - Readme, Developing, etc

Summary of changes

This is PR 2 of N (see #317):

• Adds source and source property functions that throw rather than returning a Result type.
• Removes updateSourceProperty(...), replacing it with setSourceProperty(...)
• Updates tests and examples accordingly.

[neelmistry94]

one nit about adding docs