Sliced Loading Job and Shared File Pool

[KKQ-KKQ]

@paulfd In case you are interested, I wrote this.
Feel free if you want to merge these.
I have already implemented these in isfizz.

• 1/4 Added Status FullLoaded *Already merged!
• 2/4 Sliced Loading Job
• 3/4 Use std::shared_ptr for FileData
• 4/4 Shared File Pool

Sliced Loading Job:

In this branch, the number of the File Pool threads is limited to 1.
The number of chunks loaded at once is 64 (1024*64 = 64k frames).
Without this change, there was a serious performance issue on iPad Pro when users simultaneously use other sampler plugins which do disk-streaming.

Shared File Pool

The FileData is shared with instances.
There is a memory limit on iOS/iPadOS, I added this.