Change MPL License to Apache 2.0

[dgovil]

This PR changes the MPL 2.0 license to Apache 2.0 as discussed. However, we should wait to merge this in till the following things are completed:

• [X] ILM signs off (@danrbailey to follow up)
• [X] TSC has chosen the new ASWF Standard CLA
• [X] @kmuseth said we should wait till some of the NanoVDB PRs are merged in.

I'm putting this PR up now so that I can get my own CLA squared away , and in case people want to see if I missed anything since it's a very large PR by file count.