[core] feat(Spinner): add more a11y markup, support HTML attrs

[bvandercar-vt]

Fixes #5317

Checklist

• Includes tests
• [N/A] Update documentation

Changes proposed in this pull request:

Allow custom html props to be passed to Spinner

[palantirtech]

Thanks for your interest in palantir/blueprint, @bvandercar-vt! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[bvandercar-vt]

I am on Windows 10 and am getting errors when running yarn verify/yarn compile, and cannot run yarn testeither-- can one of the Devs please check out this branch and run the test I've written plus whatever else needs to be done?

[adidahiya]

@bvandercar-vt compilation and tests look good, I got them to pass locally, and they pass in CI.

I pushed an additional commit to add more recommended aria- attributes according to the MDN documentation for role="progressbar".

[bvandercar-vt]

@bvandercar-vt compilation and tests look good, I got them to pass locally, and they pass in CI.

I pushed an additional commit to add more recommended aria- attributes according to the MDN documentation for role="progressbar".

Awesome, thanks for your help!

[adidahiya]

docs preview build here