[Rust][Experiment][WIP] Experiment with a TypedArray trait

[alamb]

Note: migrated from original JIRA: https://issues.apache.org/jira/browse/ARROW-11546

A few of the arrow kernels rely on macros to iterate over values using a common ".value()" function, but:

• this is unsafe on some array types (string, binary), but unsafe on other array types (primitive)
• this forces iteration by index, which does not always optimize away bounds-checking (at least in the binary case)

This PR is an experiment with a TypedArray trait, which provides access to array values (along with associated types describing those values).  This will NOT remove the need for downcasting, as the associated types aren't object-safe.  But it should be sufficient to allow simple processing of values from multiple array types using a generic function instead of a macro.

[tustvold]

Closed by #2133