Add encoding field to vector sources

[TimSylvester]

Adds an optional encoding field to vector sources, based on the one in raster sources, to allow the use of MapLibre Tiles.

Implementation issues:

• Native: maplibre-native #3721
• JS: maplibre-gl-js #6258

Resolves #1252

I don't think this has any effect on APIs, can someone confirm?

Launch Checklist

• Confirm your changes do not include backports from Mapbox projects (unless with compliant license)
• Briefly describe the changes in this PR.
• Link to related issues.
• Include before/after visuals or gifs if this PR includes visual changes.
• Write tests for all new functionality.
• Document any changes to public APIs.
• Post benchmark scores.
• Add an entry to CHANGELOG.md under the ## main section.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.37%. Comparing base (1768c7b) to head (e32cf89).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1251   +/-   ##
=======================================
  Coverage   95.37%   95.37%           
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  Files         114      114           
  Lines        7398     7398           
  Branches     2327     2327           
=======================================
  Hits         7056     7056           
  Misses        342      342           

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[HarelM]

Thanks for taking the time to open this PR!
Can you also please open an issue in this repo with a design proposal (basically advising to add encoding to vector source as can be understood from this PR)?

[nyurik]

Encoding focuses on "format", not the organization that produced it. mlt, mvt, ...

[louwers]

I prefer using mvt and mlt instead of mapbox and maplibre.

It is not unthinkable that either Mapbox or MapLibre releases another vector tile format in the future. Then these names would be very confusing. I already think mapbox is quite confusing because I personally don't associate MVTs with Mapbox even though they invented the format.

[HarelM]

This looks good in general.
Let's have the design proposal open for a few more days to let more people comment, and if no one has new insights we will be able to merge this.
Thanks for taking the time to open this PR and implement it!

[louwers]

@HarelM Let's merge?

[HarelM]

We need a new release of the spec package to update the docs, right?

[louwers]

No need, looks like it is live. https://maplibre.org/maplibre-style-spec/sources/#encoding

[HarelM]

Nice! Wasn't sure if docs are updated only on release or every merge to main. DevOps is awesome 😎

[acalcutt]

I am probably a bit late here, but I was looking at the MLT maplibre-js PR to get an idea of how I would implement it in tileserver-gl and was wondering about this choice to use 'encloding' instead of 'format' for the type of tile in MLT. it seems like other tile types use 'format' metadata to distinguish between what is in the tile . "encoding" seems like we only use in terrain right now, and for example in tileserver-gl it is set to either mapbox or terrarium right now. This being a vector source it is probably not much of an issue, but it seems different from the convention we have been using.

[TimSylvester]

It's just for consistency with the other source definition.