Improve capacity calculation in FileMappedResizableDirectMemory constructor

[konard]

Location: cpp/Platform.Memory/FileMappedResizableDirectMemory.h:35

Current code:

// TODO: cringe
ReservedCapacity(size > minimumReservedCapacity ? ((size / minimumReservedCapacity) + 1) * minimumReservedCapacity : minimumReservedCapacity);

Issue:
The current capacity calculation logic needs improvement. The TODO comment indicates the current implementation is suboptimal.

Suggestion:
Review and refactor the capacity calculation logic to be more readable and potentially more efficient.