[C++][Compute] Refactor FunctionExecutor -> KernelExecutor

[asfimport]

FunctionExecutor currently handles dispatch to a kernel as well as allocation and invocation of the kernel. In some contexts (such as a filter expression bound to a specific schema) we only need to perform dispatch once, so repeatedly dispatching to kernel is redundant. Refactor to a KernelExecutor which is constructed from a pre-selected kernel.

Reporter: Ben Kietzman / @bkietz
Assignee: Ben Kietzman / @bkietz

PRs and other links:

• GitHub Pull Request #8574

_{Note: This issue was originally created as ARROW-10468. Please see the migration documentation for further details.}

[asfimport]

Ben Kietzman / @bkietz:
Issue resolved by pull request 8574
#8574