Check projection instead of tiling scheme

[wallw-teal]

This allows custom tiling scheme classes by actually checking the projection in the tiling scheme rather than the tiling scheme class itself.

The use case was outlined in the forum here. However, I went ahead and changed all the places that similar checks were being done, rather than just the one I mentioned in the forum.

[cesium-concierge]

@wallw-bits, thanks for the pull request! Maintainers, we have a signed CLA from @wallw-bits, so you can review this at any time.

⚠️ I noticed that CHANGES.md has not been updated. If this change updates the public API in any way, fixes a bug, or makes any non-trivial update, please add a bullet point to CHANGES.md and comment on this pull request so we know it was updated. For more info, see the Pull Request Guidelines.

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[wallw-teal]

This should be a no-change update for Cesium itself. It only affects those attempting to use custom TilingScheme classes. Hence no update to CHANGES.md.

[hpinkos]

Thanks @wallw-bits! If this fixes a bug when you were trying to use a custom tiling scheme, you should make a note in CHANGES.md so other doing the same thing know it's fixed.

Who can review this? @kring do you have time to take a look?

[wallw-teal]

CHANGES.md updated per your request.

[kring]

Yep I'll take a look @hpinkos.

[kring]

Looks good, thanks @wallw-bits!

[cesium-concierge]

Congratulations on closing the issue! I found these Cesium forum links in the comments above:

https://groups.google.com/forum/#!topic/cesium-dev/a8hNaDBnAEw

If this issue affects any of these threads, please post a comment like the following:

The issue at #6524 has just been closed and may resolve your issue. Look for the change in the next stable release of Cesium or get it now in the master branch on GitHub https://github.com/AnalyticalGraphicsInc/cesium.

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[wallw-teal]

I think this was merged after the release was cut, which makes the CHANGES.md file incorrect on master.

Should I make another PR to fix that?

[mramato]

Good catch @wallw-bits, I fixed this directly in master so you don't have to worry about it 76d64a1

[NaderCHASER]

I believe that this fixed using NASA GIBS' Geographic Tiling Scheme (https://github.com/nasa-gibs/gibs-web-examples/blob/master/lib/gibs/gibs.js) which previously produced a blurry image at lower zoom levels. Pulling master into my fork this morning fixed this issue.

I'm now able to use a custom GibsGeographicTilingScheme.js (based on gibs.js link above) to display Blue Marble and other NASA tiles without issue, whereas before I had to use their reprojected tiles for them to display correctly in Cesium.