Optimize the operator algorithm to lazily allocate memory

Now after FLINK-14063 , operators will get all manage memory of TaskManager,  The cost of over allocate memory is very high, lead to performance regression of small batch sql jobs:

• Allocate memory will have the cost of memory management algorithm.
• Allocate memory will have the cost of memory initialization, will set all memory to zero. And this initialization will require the operating system to actually allocate physical memory.

• Over allocate memory will squash the file cache too.

We can optimize the operator algorithm, apply lazy allocation, and avoid meaningless memory allocation.