[DO NOT Merge] Very initial pass - ByteBuffer -> Memory

[niketh]

@cheddar @leventov This is a very initial pass at moving ByteBuffer -> Memory.

1. Introduced PositionMemoryRegion
2. Made changes to GenericIndexed
3. Made changes to FileSmoosher.
4. Trying to read data from Memory in indexv9loader

[leventov]

This method should be a part of Memory interface.

[leventov]

Ints.checkedCast

[leventov]

If it should exist, should be a part of the memory library, not Druid

[leventov]

Memory should be Closeable or AutoCloseable

[leventov]

In #3915 we came to agreement that Memory should be in it's small dedicated library, not datasketches

[niketh]

I thought we would like to keep Memory with DataSketches for now. I don't remember us concluding that we need to move it. What do you think @leventov @cheddar @leerho

[leventov]

@niketh sorry, wrong link. @gianm suggested that here: #3892 (comment) and I agreed here: #3892 (comment)

[leerho]

I haven't agreed. And @leventov and I are busy working out a solution that should work for both DataSketches and Druid. Let's not jump to conclusions before we determine that a fork is the only solution.

[leventov]

@leerho it is already done since apache/datasketches-java@92e67a9. and the dependency is already com.yahoo.datasketches:memory, that I missed when wrote my previous comments in this small thread.

[niketh]

@cheddar @leventov @gianm @fjy @leerho @akashdw Part 2 of the ByteBuffer -> Memory changes. There are only a few more changes left and we should have a version that will be compatible with already persisted segments. I will be posting Part 3 later this week, which should be the final one (sans code review refactoring)

[leventov]

@niketh what's the point of doing this with the old API?

[weijietong]

@niketh is this PR still underway ? please consider #3716 while doing this work .

[niketh]

@leventov @leerho @cheddar @gianm Lee has finalized the new memory interfaces yesterday. Working on moving the old Memory to the new Memory interfaces.

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