Convert LifetimeManagers to use Task<object> instead of Monitor

[ENikS]

Description

Current implementation uses Monitor for internal synchronization but native Task is significantly superior and allows better optimization.

Problem

Monitor allows simple scenarios with multithreaded access but fails in more advanced cases. It also does not allow proper async/await implementation and creates performance overhead

Solution

Lifetime managers could be converted to use Task as internal medium for storage and synchronization.

Impact

TBD.