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ARROW-17455: [Go] Function and Kernel execution architecture (#13964)

In addition to implementing the function execution architecture, this also shifts some files around for better package naming and scoping. A new package `exec` is created inside of `compute/internal/` to make it easier to scope other internal-only methods / functionality such as the kernel implementations themselves.

This is a fairly large change because so much is interconnected, but it also includes extensive tests covering ~85% of the `internal/exec` package and nearly 80% of the entire `compute` package. More tests will be added as functionality is added.

Authored-by: Matt Topol <zotthewizard@gmail.com>
Signed-off-by: Matt Topol <zotthewizard@gmail.com>