Add a ray cast API to the terrain system, implement it, and use it so entities can be placed on top of terrain. (#6895)

* Add a ray cast API to the terrain system, implement it, and use it so entities can be placed on top of terrain.

Still to do:
- Unit tests
- Profiling/benchmarks
- Optimization (if needed, may not be now after updating to use the iterative approach, but one option could be to use SIMD to ray cast against both triangles at once)

Signed-off-by: bosnichd <bosnichd@amazon.com>

* Fix typos.

Signed-off-by: bosnichd <bosnichd@amazon.com>

* Added a FindNearestIntersectionIterative to use in place of the first-pass FindnearestIntersectionRecursive attempt.

Signed-off-by: bosnichd <bosnichd@amazon.com>

* Remove some functions that are no longer being used.

Signed-off-by: bosnichd <bosnichd@amazon.com>

* Remove a unicode character from a comment to fix the validation build.

Signed-off-by: bosnichd <bosnichd@amazon.com>

* Remove another unicode character from a comment to fix the validation build.

Signed-off-by: bosnichd <bosnichd@amazon.com>

* Update to bail out as soon as t > 1.0f

Signed-off-by: bosnichd <bosnichd@amazon.com>

Code/Framework/AzToolsFramework/AzToolsFramework/Viewport/ViewportMessages.cpp

@@ -7,6 +7,7 @@
  */
 
 #include <AzFramework/Render/IntersectorInterface.h>
+#include <AzFramework/Terrain/TerrainDataRequestBus.h>
 #include <AzToolsFramework/Viewport/ViewportMessages.h>
 
 namespace AzToolsFramework
@@ -66,15 +67,19 @@ namespace AzToolsFramework
 
     AZ::Vector3 FindClosestPickIntersection(const AzFramework::RenderGeometry::RayRequest& rayRequest, const float defaultDistance)
     {
-        AzFramework::RenderGeometry::RayResult renderGeometryIntersectionResult;
+        // attempt a ray intersection with any visible mesh or terrain and return the intersection position if successful
+        AZ::EBusReduceResult<AzFramework::RenderGeometry::RayResult, AzFramework::RenderGeometry::RayResultClosestAggregator> renderGeometryIntersectionResult;
         AzFramework::RenderGeometry::IntersectorBus::EventResult(
             renderGeometryIntersectionResult, AzToolsFramework::GetEntityContextId(),
             &AzFramework::RenderGeometry::IntersectorBus::Events::RayIntersect, rayRequest);
+        AzFramework::Terrain::TerrainDataRequestBus::BroadcastResult(
+            renderGeometryIntersectionResult,
+            &AzFramework::Terrain::TerrainDataRequests::GetClosestIntersection,
+            rayRequest);
 
-        // attempt a ray intersection with any visible mesh and return the intersection position if successful
-        if (renderGeometryIntersectionResult)
+        if (renderGeometryIntersectionResult.value)
         {
-            return renderGeometryIntersectionResult.m_worldPosition;
+            return renderGeometryIntersectionResult.value.m_worldPosition;
         }
         else
         {