…ferredRegions in multiple region name formats.

This is a proposed fix for - #2330

…eep-chellappan/azure-cosmos-dotnet-v3 into pradeepc/regionname-mapping

The map table is only used on initialization, so there's no need to keep a cache of it for the lifetime of the application

The cache is created before converting all the names, so it only needs created once, but doesn't remain for the entire lifetime of the application

Instead of having a prepare/clear cache system on a static class, make RegionNameMapper a class that gets instantiated for use and let the ctor handle it.