Box2D.NET physics integration and enhancements!

Thanks again to @Happypig375, we now have Box2D.NET physics integration! You can select this as an alternative physics engine to Aether via the <add key="PhysicsEngine2d" value="Box2dNet" /> App.config entry.

However, there are some important breaking changes that might affect your serialized Nu scenes, specifically -

• GravityOverride has been renamed to Gravity and its type changed to the new Gravity DU type.
• BreakingPoint has been renamed to BreakingPointOpt.
• Joint API has removed the OneBodyJoint cases and simplified.
• Removed GetFluidParticleCellColor property.

Otherwise, we've mostly solidified the engine with minor fixes and enhancements.

Important Changes -

• Depend ground direction on gravity (when exists) or down direction relative to rotation.
• Preventing duplicate texture loading for non-dds textures in 3D.
• Exposed deferred ImGui calls via World.defer... API.
• Exposed analog controller input (#352).
• Fix normal vector in FluidEmitterMessage.
• Updated various dependencies.
• Using modern randomization methods in Gen.
• Added 2D right-up variants.
• Ability to opt-out of synchronous logging via LogSynchronously config.
• Proper editing for Justification property (#1190).
• Proper editing for FontStyling as well.
• Increased shadow texture limits to 9 for shadow textures and maps.
• Removed Release optimization that could result in NRE's in normal Nu operations.
• Plug in logging for various native dependencies.
• Implemented Gaia layout reset (#1058).
• Using imperative accumulation to enhance tile map tile placement precision.
• Fixed regression in position3dToPosition2d and otherwise.
• Added warn when render asset is unavilable.
• Added Box2dNetPhysicsEngine
• Make Nu.Math up to date with current .NET.
• Fixed job graph regression.
• Reverted character 2d changes (removed special gravity handling).
• Implemented frame stepping in Gaia via Step button.
• Fixed #1201.
• Put shadow textures in a sampler2DArray.
• No longer needlessly adding omnipresent elements to nodes (optimization).
• Fixed BreakingPoint naming (Opt suffix required).

Full Changelog: v19.7.0...v19.8.0