arrow

ARROW-9815: [Rust][DataFusion] Remove the use of Arc/Mutex to protect plan time structures

This is a continuation of the work started in https://github.com/apache/arrow/pull/8031 to clean up the `ExecutionContext` interface

Specifically, the `ExecutionContext` is used during *planning time* (not *execution time*) and thus using a `Mutex/Arc` seemed to make the code more complicated as well as suggest that they could be shared by multiple threads (which they are not).

This PR also removes several deep copies of structures, which helps readability (and likely performance in some tiny amount)

Closes #8079 from alamb/alamb/execution_context_clean_2

Authored-by: alamb <andrew@nerdnetworks.org>
Signed-off-by: Andy Grove <andygrove73@gmail.com>