Improved control over tileset LOD selection

[j9liu]

Over the years we've received various requests for more granular control over tileset selection. This issue is meant to track them all in one place.

Generalized Selection

e.g., by bounding volume, or any other means besides a camera frustum

• Add option to preload a tileset or section of a tileset #266
• Generalize tile selection beyond per-frame view frustums #1237
• Query tilesets by bounding volume at a particular LOD #1143
• Feature Request: Load 3D Tiles in dedicated server setups cesium-unreal#1826

Fixed LOD selection

i.e., fixing the level of detail that is chosen, or specifying a min/max

• Feature Request: Set Min/Max LOD cesium-unreal#1811

Higher flexibility with screen space error

• Allow local overrides of Maximum Screen Space Error on sections of tilesets cesium-unreal#323
• Per-view maximumScreenSpaceError #1399