Implement Size() measuring size estimation for execution cache

[timl3136]

What changed?
Implement Size() measuring size estimation for execution cache, add empty size estimation function for mutableState and shardContext

Why?
We want to modernize existing cadence common cache implement to a bytes-based system. That means we need to have a method to measure each entry (which is currently accepting any generic interface). We found the "Reflect" package provides a measuring function but runtime is too slow to be used in cache operations. Therefore, we will require all usages to implement the Size() function in their cache logic if they want to migrate to the new bytes-based system.

In order to seamless transition from the current cache system with an entry-based model, the implementation and rollout will be done in following phases:

1. Define the Sizeable interface
2. Implement Sizeable for cadence-history service
   a. Implement Size() for ExecutionCache <-- This PR
   b. Implement Size() for EventCache
3. Implement bytes-based cache system
4. Enable new cache system for usage in cadence-history service
5. Implement and enable new cache system for the remaining usages

How did you test it?
Unit tests

Potential risks
No risk since this PR only adds read-only function that is not used.

Release notes

Documentation Changes

[davidporter-id-au]

I'm not sure if you have a Size interface somewhere, but would it make more sense for using that?

The thing about creating an interface for Size() int is that it'll allow whatever caches that need to take inputs can just require the interface, rather than any specific concrete types?

[timl3136]

That makes sense, I will change the naming to Size(). Thanks.