Add unit test for DB creation with unicode path

Summary:

An issue arose when attempting to switch back to the main repo version of leveldb when the bitcoin data directory uses a unicode path. The leveldb windows file IO wrapper was using the *A ANSI win32 calls instead of the Unicode *W ones. This unit test will catch if the path created by leveldb doesn't match what we're expecting. For more info see https://github.com/google/leveldb/issues/755.

This is a backport of Core PR17641

Test Plan: ninja && ninja check

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D8285