perf(mapcache): Simplify and improve implementation of MapCache to prevent expensive reoccurring redundant map cache reads

[xezon]

This change simplifies and improves the implementation of MapCache to prevent expensive reoccurring redundant map cache reads. It also removes DEBUG_LOG in buildMapListForNumPlayers because it is a spammy log that adds stalling.

Originally, the implementation in MapCache::updateCache was a total munkee disaster. Very complicated and inefficient. This change turned out to be half refactor, half performance optimization.

Problems in MapCache were:

• Standard and User Map Cache INI loaded on every call to MapCache::updateCache, even if already loaded
• Too much different logic cramped into MapCache::loadUserMaps
• Overcomplicated logic around TheGlobalData->m_buildMapCache
• Overcomplicated and inefficient logic around std::map<AsciiString, Bool> m_seen
• Standard Maps Cache built in two code paths
• Standard Maps Cache built after existing Cache was already loaded, causing poisened Map Cache generation

All this is fixed.

Performance measurement

Measured in optimized vs2022 build, with RTS_DEBUG.

Map List Click	Original Time	Optimized Time (This Change)
System Maps	203 ms	62 ms
User Maps	313 ms	62 ms

TODO

• Replicate in Generals