EntityLock<> and Optional<> lock permission, and early lock release optimization

[xthexder]

EntityLock<ECS, Permissions...> is a new lock type that is roughly equivalent to a std::pair<Lock<ECS, Permissions...>, Entity>.
This lock type can be used to perform parallel writes to multiple entities within a single transaction, while allowing reads to all entities.
Reads of values on entities not covered by the lock see the value as of the start of the transaction, with changes to other entities hidden until the transaction completes.

The Optional<> lock permission replaces DynamicLock<>, and allows for any existing Lock<ECS, Permissions...> to be declared as optional and checked at runtime.

Locks now properly reference count each component individually, allowing read-only lock permissions to be released early if a lock has been converted to a subset, and no more references to that component exist.
ECS component storage also has a new WriteToReadLock call, which allows a Write permission to be downgraded to Read permissions without starting a new transaction.