arrow

ARROW-4628: [Rust] [DataFusion] Implement type coercion query optimizer rule

This PR refactors the existing type coercion logic, to remove it from the SQL query planner and into an optimizer rule and also makes it more complete, with improved unit tests.

It also converts more functions to return Result instead of using unwrap and removes some dead code and removes some duplicated code by introducing a new `utils` file in `optimizer` module.

Author: Andy Grove <andygrove73@gmail.com>

Closes #3939 from andygrove/type_coercion and squashes the following commits:

d94d8fdb <Andy Grove> use correct error type
f8b25e9e <Andy Grove> manual merge with latest from master
30ef3396 <Andy Grove> rebase
98447920 <Andy Grove> Roll back some changes to reduce scope of PR
1a76ca3b <Andy Grove> Implement type coercion optimizer rule