Replace usages of assertArrayEquals, deprecate it

Problem/Motivation

UnitTestCase::assertArrayEquals seems redundant now - PHPUnit's provided assertEquals method is actually doing a per-key comparison in associative arrays by default; in case the structure matters assertSame can do, and in case of simple arrays assertEqualsCanonicalizing can be used to pre-sort values before comparison.

Proposed resolution

Deprecate assertArrayEquals and replace its usages with standard PHPUnit methods.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet