Speed up session loader

[soulomoon]

Session loader is responsible for generating ghc options to load modules. Due to the limitation of hie-bios, we are loading module one by one. The session loader is overly sequentialized.

Problems:

1. Not loading in batch with multi homeunit support. Initial load of multiple home units is slow with lazy component loading #4381
2. Loading of a module's options is blocked by the loading in the front of the line even if the module's options in the cache.

Solutions:

1. Batch load. SessionLoader: batch load #4439
2. Decouple the session loader into reader and writer over the cache. Decouple the session loader into reader and writer over the cache #4445