Emoji don't work in TextFields using Oracle backend

[dmedvinsky]

When using cx_Oracle as a backend, I can't use Emoji in TextFields, which are stored as NCLOBs in the database. When inputting an emoji and saving them in the database, upon retrieving I get four replacement charaters (�) per emoji instead.

Django ​uses hardcoded NLS_LANG=".UTF8" variable, which is outdated, only supports Unicode standard version 3 and cannot properly store 4-byte characters. ​The Oracle documentation recommends using the AL32UTF8 encoding instead, which supports latest Unicode standard and stores 4-byte characters properly.

The change that fixes the emoji for me: ​https://github.com/django/django/pull/7241

I recognize that it needs some tests, so I seek the help from those with better knowledge of Django test cases than me. If someone can kindly direct me, I can create the test for this case.

[Tim Graham]

The new tests don't pass on MySQL due to #18392. We can either fix that issue first, or skip the test on MySQL.

[Tim Graham <timograham@…>]

In 1a9f6db5:

Fixed #27219 -- Changed cx_Oracle client encoding to AL32UTF8 to allow 4-byte characters.