Add transformCameraUpdate callback

[Pessimistress]

For #1545

Change List

• Add transformCameraUpdate option to Map
• Inject _startCameraUpdate and _endCameraUpdate into the following methods where Camera.transform is modified:
  • Camera.jumpTo
  • Camera.easeTo
  • Camera.flyTo
  • HandlerManager._updateMapTransform
    See inline comments
• A helper class HandlerBase for handlers to access the correct camera state

There should be no behavioral change or performance overhead if transformCameraUpdate is not assigned.

Launch Checklist

• Confirm your changes do not include backports from Mapbox projects (unless with compliant license) - if you are not sure about this, please ask!
• 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.

[birkskyum]

To see how this PR worked in practice, I made a debug page here (it can be dumped next to the other, if this PR branch is checked out):
https://github.com/birkskyum/maplibre-gl-js/blob/transform-camera-update/test/debug-pages/reactive.html

I think it works as expected, with minimal change to our public API, and if I'm not mistaken it doesn't see to contain any breaking changes. Here is a small clip of the left map driving the right, without constantly lagging a frame behind.

Screen.Recording.2023-05-16.at.12.40.03.mov

mis click, some naming is needed

[birkskyum]

This little hook has surprisingly great utility - should not be overlooked.

• Without a js framework (like the debug-pages i made) it's possible to use gl js in a reactive way.
• All JS frameworks (react, vue, svelte, solid, angular etc.), especially where a wrapper isn't available, will get better ergonomics. You can finally get the direct camera values synced to a store, and they are not lagging 1 frame behind - terrain makes this even more important when the camera 'jumps' over a peak as that camera value wasn't possible to get at all.
• Advanced wrappers (the list is growing) like react-map-gl, ngx-maplibre-gl, deckgl, maptiler-sdk-js, will have a much easier time dealing with the camera.
  @wipfli , fyi

[HarelM]

@Pessimistress thanks for taking the time to open this PR!
I think there are still some naming and small fixes left to do, but this looks great in general.

[Pessimistress]

Some renames according to review comments:

• Transform.copy(that: Transform) -> Transform.apply(that: Transform)
• Camera._transformCameraUpdate -> Camera.transformCameraUpdate
• Camera._transformInProgress; -> Camera._requestedCameraState
• Camera._startCameraUpdate(): Transform -> Camera._getTransformForUpdate(): Transform
• Camera._endCameraUpdate(tr: Transform) -> Camera._applyUpdatedTransform(tr: Transform)

I don't think transformCameraUpdate is necessarily confusing because the internal term "transform" as a camera/viewport is not exposed to the end user. There's already an option transformRequest that does a similar thing (intercept arguments and modify them before use).

How concerned are you about the bundle size?

[HarelM]

How concerned are you about the bundle size?

Not really concerned. Please update the size in the test.
Overall looks good. THANKS!

[birkskyum]

Thanks for the renaming, i find this easier to reason about. We need a changelog entry.

[birkskyum]

Great job!