Addressed light map adjustments resulting in no net change dirtying c…

[PatrikLundell]

…ache

Summary

None

Purpose of change

Fix #77026, i.e. sleeping near furniture slowing game to a craw.

Describe the solution

Change the light map -> vision map modification to only dirty the cache on a change of the cache state rather than on any modification of the light map data even when the result to the vision cache is not changed.

Describe alternatives you've considered

Testing

• Slept in a shelter next to a table (the bug report test situation that was slow previously).
• Slept near a tree (don't know if it was slow before, as make the game faster when player sleep near the tree #73590 tried to address that).
• Debug changed the time to about 18:00 next day to get daylight, laid down, and waited for 3 hours. The light level changed over time as expected.
• Debug spawned a church, teleported to it, debug changed time to about 18:00 the next day (daylight waning, again), laid down on the floor (shouldn't matter), waited for 1 hour and saw the light change (at a decent clip). The point here is that the stained windows ought to have slowed down the previous implementation (but haven't verified if that's the case).

There ought to be other situations that should be tested, but I can't come up with any.

Additional context

There is always the risk that I've misunderstood how the caches work or are used.