Docs for rasterarray source

This PR adds JSDocs comment for rasterarray source

Launch Checklist

[x] Make sure the PR title is descriptive and preferably reflects the change from the user's perspective.
[x] Add additional detail and context in the PR description (with screenshots/videos if there are visual changes).
[ ] Manually test the debug page.
[ ] Write tests for all new functionality and make sure the CI checks pass.
[ ] Document any changes to public APIs.
[ ] Post benchmark scores if the change could affect performance.
[ ] Tag @mapbox/map-design-team @mapbox/static-apis if this PR includes style spec API or visual changes.
[ ] Tag @mapbox/gl-native if this PR includes shader changes or needs a native port.