Data formatters: Look through array element typedefs

Summary:
Motivation: When formatting an array of typedefed chars, we would like to display the array as a string.

The string formatter currently does not trigger because the formatter lookup does not resolve typedefs for array elements (this behavior is inconsistent with pointers, for those we do look through pointee typedefs). This patch tries to make the array formatter lookup somewhat consistent with the pointer formatter lookup.

Reviewers: teemperor, clayborg

Reviewed By: teemperor, clayborg

Subscribers: clayborg, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D72133