[EPIC] Make generation independent from requested region

[KurbyDoo]

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Same as title

Milestones

Region requests need to be expanded to match a multiple of a window size

• If we have window size 5x5 and a user requests a window of size 3x3, expand it to 5x5

Make windows and the location of generated patches based on a global world grid rather than region local space

• If I ask to generate 10 different regions that overlap with the window at the origin, then all of those regions should generate the same window
• This allows us to cache already generated windows in the terrain store

Crop generated value back to requested size

• The 5x5 window generated in step 1 should be truncated back to 3x3