Vector tile drawing for .mvt and .pbf format

[vershwal]

Related #3742.

[geohacker]

Nice work @vershwal! 👏

Let's outline what this PR contains for the time being - this add .mvt support by converting the tile to geojson and rendering them on the map. We'll use this internally to integrate a vector tile URL or an mbtiles file in the next sprint.

[vershwal]

if a user uploads some unknown format or broken file, some kind of error message would be incredibly helpful to find out what's going on.

Ya, this sounds good! Will do that. Thanks.

[bhousel]

Thanks @vershwal this is a great start!

Quick update on this - I changed a few things below and merged the code:

• I replaced d3_fetch (a newer API which isn't supported on IE11) with d3_request (traditional XHR)
• There are still some todos in the code
• I commented out the item from the map data panel.

Next action for me:

• We really should just combine the "gpx" and "mvt" layers into a single module which handles all overlay data. They each currently register a drag-and-drop handler and these handlers are conflicting with each other. Also they have misleading names. And it's just redundant and confusing to have two things. So I'm going to combine them 😅

Next action for @vershwal :
So the code was merged but is commented out and not ready yet. I didn't want your PR to diverge too much from master. The vershwal:check branch was not really current when you started the work, so that's why the merge above did some weird things to the PR. Going forward I'd like to work more disciplined like this:

• set main iD repo as your origin remote (you are a collaborator so this is ok)
  git remote set-url origin git@github.com:openstreetmap/iD.git
• pull from master frequently, but avoid developing on that branch or pushing to it
  git checkout master && git pull origin master
• create feature branches off of master before working on something
  git checkout -b new_thing
• try to check in a little bit of work every day, and push to your feature branch.
  git push origin new_thing

We can chat on Slack more if you have questions!

[vershwal]

Hey @bhousel !! Thanks for the merge and comments.
I generally try to follow all these steps. Tere were a lot of changes in the master branch during my work in this PR so there were many merge conflicts and things got complicated.
I'll take care of this for the next time.
Thanks.