I was expecting the code here to use the expression value of projection, is it using the expression value somewhere that I have missed?

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Project coverage is 89.27%. Comparing base (8555091) to head (63b317f).
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@HarelM , there is some preparation work needed in GL JS before this can be hooked up to the map style.

I think the best take on it is to make this PR just an "'update style-spec", allowing the createExpression to work. Then we can refactor incrementally on the main branch, until we can hook it up to the map.style, and only then make the changelog item for the new feature. Do you think that can work?

For example, I see some issues with tile loading, when going between projections:

And if terrain is enabled, the globe/vertical-perspective fog appear to break things.

• Support Fog in Vertical Perspective with Terrain #4985
• Fix terrain fog on globe #4924

Also, the vertical-perspective projection, in the setProjection, it doesn't take a globeness value that we can use to pass in the transition.

Also there could be some perf here, where we maybe should update the globeness in the existing projection instance, instead of making a lot of new Projection instances.

Spec package will be updated automatically in a few days by dependabot.
If there are other changes related to this package update then it should be part of this PR I guess.
Other existing bugs not related to the sec change should be handled regardless of this change.

Sounds good, I'll leave it to dependabot to make the version change (thought it didn't handled major-release updates).