Add dragInertia options for custom drag panning

[aMoniker]

This PR Adds dragInertia options to the base map options.

I don't know if this exposes too many options, and/or if there should be another option for setting velocity directly. I also don't know if I'm following convention as this is my first PR to the codebase. Happy to change what's needed.

I haven't written tests for this yet, but can once the idea & options format is considered acceptable. Likewise for public API documentation & benchmarks.

Fixes #4851

Launch Checklist

• briefly describe the changes in this PR
• write tests for all new functionality
• document any changes to public APIs
• post benchmark scores
• manually test the debug page

[arindam1993]

Thanks for the PR @aMoniker 😃

I think it looks good for the most part, but I think a cleaner api would be to allow setting these properties on options.dragPan, the truthy-ness can be used to activate/deactivate the handler, and the data can be used to configure it.

[arindam1993]

Closing since these changes have been integrated into #8887, thanks @aMoniker!

[aMoniker]

Nice work, thanks @arindam1993