Dynamic work scheduling in FileStream

[alamb]

Stacked on

• Rewrite FileStream in terms of Morsel API #21342
  Which is then stacked on
• Introduce Morselizer API #21327
• Split FileStreamMetrics into its own module #21340

Which issue does this PR close?

• part of Introduce morsel-driven Parquet scan #20529
• Broken out of Sketch out a Morselize API #20820

Rationale for this change

The whole point of this sequence of PRs is to enable dynamic work scheduling in the FileStream (so that if a task is done it can look at any remaining work)

What changes are included in this PR?

1. Add shared state to FileStream for siblings
2. Sibling streams put their file work into a shared queue when it can be reordered

Note there are a bunch of other things that are NOT included in this PR, including

1. Trying to limit concurrent IO (this PR has the same properties as main -- up to one outstanding IO per partition)
2. Trying to issue multiple IOs by the same partition (aka to interleave IO and CPU work)

Are these changes tested?

Yes by existing functional and benchmark tests, as well as new functional tests

Are there any user-facing changes?

Yes, faster performance (TODO MEASURE)