Deprecated FloatingPawn and CesiumGlobeAnchorParent

[xuelongmu]

Closes #450

Reference for deprecation symbols: https://ikrima.dev/ue4guide/engine-programming/uobjects/deprecating-uproperties-ufunctions/

See notes at #450 (comment)

[cesium-concierge]

Thanks for the pull request @xuelongmu!

• ✔️ Signed CLA found.

Reviewers, don't forget to make sure that:

• Cesium for Unreal Samples works.

[kring]

This looks good to me. I confirmed that cesium-unreal-samples, which of course includes a FloatingPawn, pops up a message when it's loaded but otherwise still works correctly. The message says:

LoadErrors: Warning: FloatingPawn_C /Game/CesiumSamples/Maps/01/01_CesiumWorld.01_CesiumWorld:PersistentLevel.FloatingPawn_18: class /CesiumForUnreal/FloatingPawn.FloatingPawn_C has been deprecated.

[xuelongmu]

I did some testing today and can confirm that the warning shows up, but floating pawn still works correctly. Additionally, if you try to compile the deprecated blueprint, it'll fail to compile, and afterwards if you try to play in-game there will be a BLUEPRINT COMPILE ERROR log message that shows up in the top left, but again this doesn't seem to affect the functionality. 👍